spring-boot-features.adoc

Spring Boot features

SpringApplication

The SpringApplication class provides a convenient way to bootstrap a Spring application that will be started from a main() method. In many situations you can just delegate to the static SpringApplication.run method:

public static void main(String[] args) {
	SpringApplication.run(MySpringConfiguration.class, args);
}

When your application starts you should see something similar to the following:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::   v{spring-boot-version}

2013-07-31 00:08:16.117  INFO 56603 --- [           main] o.s.b.s.app.SampleApplication            : Starting SampleApplication v0.1.0 on mycomputer with PID 56603 (/apps/myapp.jar started by pwebb)
2013-07-31 00:08:16.166  INFO 56603 --- [           main] ationConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@6e5a8246: startup date [Wed Jul 31 00:08:16 PDT 2013]; root of context hierarchy
2014-03-04 13:09:54.912  INFO 41370 --- [           main] .t.TomcatServletWebServerFactory : Server initialized with port: 8080
2014-03-04 13:09:56.501  INFO 41370 --- [           main] o.s.b.s.app.SampleApplication            : Started SampleApplication in 2.992 seconds (JVM running for 3.658)

By default INFO logging messages will be shown, including some relevant startup details such as the user that launched the application.

Startup failure

If your application fails to start, registered FailureAnalyzers get a chance to provide a dedicated error message and a concrete action to fix the problem. For instance if you start a web application on port 8080 and that port is already in use, you should see something similar to the following:

***************************
APPLICATION FAILED TO START
***************************

Description:

Embedded servlet container failed to start. Port 8080 was already in use.

Action:

Identify and stop the process that's listening on port 8080 or configure this application to listen on another port.

Note	Spring Boot provides numerous FailureAnalyzer implementations and you can add your own very easily.

If no failure analyzers are able to handle the exception, you can still display the full auto-configuration report to better understand what went wrong. To do so you need to enable the debug property or enable DEBUG logging for org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer.

For instance, if you are running your application using java -jar you can enable the debug property as follows:

$ java -jar myproject-0.0.1-SNAPSHOT.jar --debug

Customizing the Banner

The banner that is printed on start up can be changed by adding a banner.txt file to your classpath, or by setting banner.location to the location of such a file. If the file has an unusual encoding you can set banner.charset (default is UTF-8). In addition to a text file, you can also add a banner.gif, banner.jpg or banner.png image file to your classpath, or set a banner.image.location property. Images will be converted into an ASCII art representation and printed above any text banner.

Inside your banner.txt file you can use any of the following placeholders:

Table 1. Banner variables

Variable	Description
${application.version}	The version number of your application as declared in MANIFEST.MF. For example Implementation-Version: 1.0 is printed as 1.0.
${application.formatted-version}	The version number of your application as declared in MANIFEST.MF formatted for display (surrounded with brackets and prefixed with v). For example (v1.0).
${spring-boot.version}	The Spring Boot version that you are using. For example {spring-boot-version}.
${spring-boot.formatted-version}	The Spring Boot version that you are using formatted for display (surrounded with brackets and prefixed with v). For example (v{spring-boot-version}).
${Ansi.NAME} (or ${AnsiColor.NAME}, ${AnsiBackground.NAME}, ${AnsiStyle.NAME})	Where NAME is the name of an ANSI escape code. See {sc-spring-boot}/ansi/AnsiPropertySource.{sc-ext}[AnsiPropertySource] for details.
${application.title}	The title of your application as declared in MANIFEST.MF. For example Implementation-Title: MyApp is printed as MyApp.

Tip	The SpringApplication.setBanner(…​) method can be used if you want to generate a banner programmatically. Use the org.springframework.boot.Banner interface and implement your own printBanner() method.

You can also use the spring.main.banner-mode property to determine if the banner has to be printed on System.out (console), using the configured logger (log) or not at all (off).

The printed banner will be registered as a singleton bean under the name springBootBanner.

Note	YAML maps off to false so make sure to add quotes if you want to disable the banner in your application. spring: main: banner-mode: "off"

Customizing SpringApplication

If the SpringApplication defaults aren’t to your taste you can instead create a local instance and customize it. For example, to turn off the banner you would write:

public static void main(String[] args) {
	SpringApplication app = new SpringApplication(MySpringConfiguration.class);
	app.setBannerMode(Banner.Mode.OFF);
	app.run(args);
}

Note	The constructor arguments passed to SpringApplication are configuration sources for spring beans. In most cases these will be references to @Configuration classes, but they could also be references to XML configuration or to packages that should be scanned.

It is also possible to configure the SpringApplication using an application.properties file. See Externalized Configuration for details.

For a complete list of the configuration options, see the {dc-spring-boot}/SpringApplication.{dc-ext}[SpringApplication Javadoc].

Fluent builder API

If you need to build an ApplicationContext hierarchy (multiple contexts with a parent/child relationship), or if you just prefer using a ‘fluent’ builder API, you can use the SpringApplicationBuilder.

The SpringApplicationBuilder allows you to chain together multiple method calls, and includes parent and child methods that allow you to create a hierarchy.

For example:

link:{code-examples}/builder/SpringApplicationBuilderExample.java[role=include]

Note

There are some restrictions when creating an ApplicationContext hierarchy, e.g. Web components must be contained within the child context, and the same Environment will be used for both parent and child contexts. See the {dc-spring-boot}/builder/SpringApplicationBuilder.{dc-ext}[SpringApplicationBuilder Javadoc] for full details.

Application events and listeners

In addition to the usual Spring Framework events, such as {spring-javadoc}/context/event/ContextRefreshedEvent.{dc-ext}[ContextRefreshedEvent], a SpringApplication sends some additional application events.

Note

Some events are actually triggered before the ApplicationContext is created so you cannot register a listener on those as a @Bean. You can register them via the SpringApplication.addListeners(…​) or SpringApplicationBuilder.listeners(…​) methods. If you want those listeners to be registered automatically regardless of the way the application is created you can add a META-INF/spring.factories file to your project and reference your listener(s) using the org.springframework.context.ApplicationListener key. org.springframework.context.ApplicationListener=com.example.project.MyListener

Application events are sent in the following order, as your application runs:

1. An ApplicationStartingEvent is sent at the start of a run, but before any processing except the registration of listeners and initializers.

2. An ApplicationEnvironmentPreparedEvent is sent when the Environment to be used in the context is known, but before the context is created.

3. An ApplicationPreparedEvent is sent just before the refresh is started, but after bean definitions have been loaded.

4. An ApplicationReadyEvent is sent after the refresh and any related callbacks have been processed to indicate the application is ready to service requests.

5. An ApplicationFailedEvent is sent if there is an exception on startup.

Tip	You often won’t need to use application events, but it can be handy to know that they exist. Internally, Spring Boot uses events to handle a variety of tasks.

Web environment

A SpringApplication will attempt to create the right type of ApplicationContext on your behalf. By default, an AnnotationConfigApplicationContext or AnnotationConfigServletWebServerApplicationContext will be used, depending on whether you are developing a web application or not.

The algorithm used to determine a ‘web environment’ is fairly simplistic (based on the presence of a few classes). You can use setWebEnvironment(boolean webEnvironment) if you need to override the default.

It is also possible to take complete control of the ApplicationContext type that will be used by calling setApplicationContextClass(…​).

Tip	It is often desirable to call setWebEnvironment(false) when using SpringApplication within a JUnit test.

Accessing application arguments

If you need to access the application arguments that were passed to SpringApplication.run(…​) you can inject a org.springframework.boot.ApplicationArguments bean. The ApplicationArguments interface provides access to both the raw String[] arguments as well as parsed option and non-option arguments:

import org.springframework.boot.*
import org.springframework.beans.factory.annotation.*
import org.springframework.stereotype.*

@Component
public class MyBean {

	@Autowired
	public MyBean(ApplicationArguments args) {
		boolean debug = args.containsOption("debug");
		List<String> files = args.getNonOptionArgs();
		// if run with "--debug logfile.txt" debug=true, files=["logfile.txt"]
	}

}

Tip	Spring Boot will also register a CommandLinePropertySource with the Spring Environment. This allows you to also inject single application arguments using the @Value annotation.

Using the ApplicationRunner or CommandLineRunner

If you need to run some specific code once the SpringApplication has started, you can implement the ApplicationRunner or CommandLineRunner interfaces. Both interfaces work in the same way and offer a single run method which will be called just before SpringApplication.run(…​) completes.

The CommandLineRunner interfaces provides access to application arguments as a simple string array, whereas the ApplicationRunner uses the ApplicationArguments interface discussed above.

import org.springframework.boot.*
import org.springframework.stereotype.*

@Component
public class MyBean implements CommandLineRunner {

	public void run(String... args) {
		// Do something...
	}

}

You can additionally implement the org.springframework.core.Ordered interface or use the org.springframework.core.annotation.Order annotation if several CommandLineRunner or ApplicationRunner beans are defined that must be called in a specific order.

Application exit

Each SpringApplication will register a shutdown hook with the JVM to ensure that the ApplicationContext is closed gracefully on exit. All the standard Spring lifecycle callbacks (such as the DisposableBean interface, or the @PreDestroy annotation) can be used.

In addition, beans may implement the org.springframework.boot.ExitCodeGenerator interface if they wish to return a specific exit code when the application ends.

Admin features

It is possible to enable admin-related features for the application by specifying the spring.application.admin.enabled property. This exposes the {sc-spring-boot}/admin/SpringApplicationAdminMXBean.{sc-ext}[SpringApplicationAdminMXBean] on the platform MBeanServer. You could use this feature to administer your Spring Boot application remotely. This could also be useful for any service wrapper implementation.

Tip	If you want to know on which HTTP port the application is running, get the property with key local.server.port.

Note	Take care when enabling this feature as the MBean exposes a method to shutdown the application.

Externalized Configuration

Spring Boot allows you to externalize your configuration so you can work with the same application code in different environments. You can use properties files, YAML files, environment variables and command-line arguments to externalize configuration. Property values can be injected directly into your beans using the @Value annotation, accessed via Spring’s Environment abstraction or bound to structured objects via @ConfigurationProperties.

Spring Boot uses a very particular PropertySource order that is designed to allow sensible overriding of values. Properties are considered in the following order:

1. Devtools global settings properties on your home directory (~/.spring-boot-devtools.properties when devtools is active).

2. {spring-javadoc}/test/context/TestPropertySource.{dc-ext}[@TestPropertySource] annotations on your tests.

3. {dc-spring-boot-test}/context/SpringBootTest.{dc-ext}[@SpringBootTest#properties] annotation attribute on your tests.

4. Command line arguments.

5. Properties from SPRING_APPLICATION_JSON (inline JSON embedded in an environment variable or system property)

6. ServletConfig init parameters.

7. ServletContext init parameters.

8. JNDI attributes from java:comp/env.

9. Java System properties (System.getProperties()).

10. OS environment variables.

11. A RandomValuePropertySource that only has properties in random.*.

12. Profile-specific application properties outside of your packaged jar (application-{profile}.properties and YAML variants)

13. Profile-specific application properties packaged inside your jar (application-{profile}.properties and YAML variants)

14. Application properties outside of your packaged jar (application.properties and YAML variants).

15. Application properties packaged inside your jar (application.properties and YAML variants).

16. {spring-javadoc}/context/annotation/PropertySource.{dc-ext}[@PropertySource] annotations on your @Configuration classes.

17. Default properties (specified using SpringApplication.setDefaultProperties).

To provide a concrete example, suppose you develop a @Component that uses a name property:

import org.springframework.stereotype.*
import org.springframework.beans.factory.annotation.*

@Component
public class MyBean {

    @Value("${name}")
    private String name;

    // ...

}

On your application classpath (e.g. inside your jar) you can have an application.properties that provides a sensible default property value for name. When running in a new environment, an application.properties can be provided outside of your jar that overrides the name; and for one-off testing, you can launch with a specific command line switch (e.g. java -jar app.jar --name="Spring").

Tip

The SPRING_APPLICATION_JSON properties can be supplied on the command line with an environment variable. For example in a UN*X shell: $ SPRING_APPLICATION_JSON='{"foo":{"bar":"spam"}}' java -jar myapp.jar In this example you will end up with foo.bar=spam in the Spring Environment. You can also supply the JSON as spring.application.json in a System variable: $ java -Dspring.application.json='{"foo":"bar"}' -jar myapp.jar or command line argument: $ java -jar myapp.jar --spring.application.json='{"foo":"bar"}' or as a JNDI variable java:comp/env/spring.application.json.

Configuring random values

The RandomValuePropertySource is useful for injecting random values (e.g. into secrets or test cases). It can produce integers, longs, uuids or strings, e.g.

my.secret=${random.value}
my.number=${random.int}
my.bignumber=${random.long}
my.uuid=${random.uuid}
my.number.less.than.ten=${random.int(10)}
my.number.in.range=${random.int[1024,65536]}

The random.int* syntax is OPEN value (,max) CLOSE where the OPEN,CLOSE are any character and value,max are integers. If max is provided then value is the minimum value and max is the maximum (exclusive).

Accessing command line properties

By default SpringApplication will convert any command line option arguments (starting with ‘--’, e.g. --server.port=9000) to a property and add it to the Spring Environment. As mentioned above, command line properties always take precedence over other property sources.

If you don’t want command line properties to be added to the Environment you can disable them using SpringApplication.setAddCommandLineProperties(false).

Application property files

SpringApplication will load properties from application.properties files in the following locations and add them to the Spring Environment:

1. A /config subdirectory of the current directory.

2. The current directory

3. A classpath /config package

4. The classpath root

The list is ordered by precedence (properties defined in locations higher in the list override those defined in lower locations).

Note	You can also use YAML ('.yml') files as an alternative to '.properties'.

If you don’t like application.properties as the configuration file name you can switch to another by specifying a spring.config.name environment property. You can also refer to an explicit location using the spring.config.location environment property (comma-separated list of directory locations, or file paths).

$ java -jar myproject.jar --spring.config.name=myproject

or

$ java -jar myproject.jar --spring.config.location=classpath:/default.properties,classpath:/override.properties

Warning

spring.config.name and spring.config.location are used very early to determine which files have to be loaded so they have to be defined as an environment property (typically OS env, system property or command line argument).

If spring.config.location contains directories (as opposed to files) they should end in / (and will be appended with the names generated from spring.config.name before being loaded, including profile-specific file names). Files specified in spring.config.location are used as-is, with no support for profile-specific variants, and will be overridden by any profile-specific properties.

The default search path classpath:,classpath:/config,file:,file:config/ is always used, irrespective of the value of spring.config.location. This search path is ordered from lowest to highest precedence (file:config/ wins). If you do specify your own locations, they take precedence over all of the default locations and use the same lowest to highest precedence ordering. In that way you can set up default values for your application in application.properties (or whatever other basename you choose with spring.config.name) and override it at runtime with a different file, keeping the defaults.

Note	If you use environment variables rather than system properties, most operating systems disallow period-separated key names, but you can use underscores instead (e.g. SPRING_CONFIG_NAME instead of spring.config.name).

Note	If you are running in a container then JNDI properties (in java:comp/env) or servlet context initialization parameters can be used instead of, or as well as, environment variables or system properties.

Profile-specific properties

In addition to application.properties files, profile-specific properties can also be defined using the naming convention application-{profile}.properties. The Environment has a set of default profiles (by default [default]) which are used if no active profiles are set (i.e. if no profiles are explicitly activated then properties from application-default.properties are loaded).

Profile-specific properties are loaded from the same locations as standard application.properties, with profile-specific files always overriding the non-specific ones irrespective of whether the profile-specific files are inside or outside your packaged jar.

If several profiles are specified, a last wins strategy applies. For example, profiles specified by the spring.profiles.active property are added after those configured via the SpringApplication API and therefore take precedence.

Note	If you have specified any files in spring.config.location, profile-specific variants of those files will not be considered. Use directories in spring.config.location if you also want to also use profile-specific properties.

Placeholders in properties

The values in application.properties are filtered through the existing Environment when they are used so you can refer back to previously defined values (e.g. from System properties).

app.name=MyApp
app.description=${app.name} is a Spring Boot application

Tip	You can also use this technique to create ‘short’ variants of existing Spring Boot properties. See the howto.adoc how-to for details.

Using YAML instead of Properties

YAML is a superset of JSON, and as such is a very convenient format for specifying hierarchical configuration data. The SpringApplication class will automatically support YAML as an alternative to properties whenever you have the SnakeYAML library on your classpath.

Note	If you use ‘Starters’ SnakeYAML will be automatically provided via spring-boot-starter.

Loading YAML

Spring Framework provides two convenient classes that can be used to load YAML documents. The YamlPropertiesFactoryBean will load YAML as Properties and the YamlMapFactoryBean will load YAML as a Map.

For example, the following YAML document:

environments:
	dev:
		url: http://dev.bar.com
		name: Developer Setup
	prod:
		url: http://foo.bar.com
		name: My Cool App

Would be transformed into these properties:

environments.dev.url=http://dev.bar.com
environments.dev.name=Developer Setup
environments.prod.url=http://foo.bar.com
environments.prod.name=My Cool App

YAML lists are represented as property keys with [index] dereferencers, for example this YAML:

my:
servers:
	- dev.bar.com
	- foo.bar.com

Would be transformed into these properties:

my.servers[0]=dev.bar.com
my.servers[1]=foo.bar.com

To bind to properties like that using the Spring DataBinder utilities (which is what @ConfigurationProperties does) you need to have a property in the target bean of type java.util.List (or Set) and you either need to provide a setter, or initialize it with a mutable value, e.g. this will bind to the properties above

@ConfigurationProperties(prefix="my")
public class Config {

	private List<String> servers = new ArrayList<String>();

	public List<String> getServers() {
		return this.servers;
	}
}

Note

Extra care is required when configuring lists that way as overriding will not work as you would expect. In the example above, when my.servers is redefined in several places, the individual elements are targeted for override, not the list. To make sure that a PropertySource with higher precedence can override the list, you need to define it as a single property: my: servers: dev.bar.com,foo.bar.com

Exposing YAML as properties in the Spring Environment

The YamlPropertySourceLoader class can be used to expose YAML as a PropertySource in the Spring Environment. This allows you to use the familiar @Value annotation with placeholders syntax to access YAML properties.

Multi-profile YAML documents

You can specify multiple profile-specific YAML documents in a single file by using a spring.profiles key to indicate when the document applies. For example:

server:
	address: 192.168.1.100
---
spring:
	profiles: development
server:
	address: 127.0.0.1
---
spring:
	profiles: production
server:
	address: 192.168.1.120

In the example above, the server.address property will be 127.0.0.1 if the development profile is active. If the development and production profiles are not enabled, then the value for the property will be 192.168.1.100.

The default profiles are activated if none are explicitly active when the application context starts. So in this YAML we set a value for security.user.password that is only available in the "default" profile:

server:
  port: 8000
---
spring:
  profiles: default
security:
  user:
    password: weak

whereas in this example, the password is always set because it isn’t attached to any profile, and it would have to be explicitly reset in all other profiles as necessary:

server:
  port: 8000
security:
  user:
    password: weak

Spring profiles designated using the "spring.profiles" element may optionally be negated using the ! character. If both negated and non-negated profiles are specified for a single document, at least one non-negated profile must match and no negated profiles may match.

YAML shortcomings

YAML files can’t be loaded via the @PropertySource annotation. So in the case that you need to load values that way, you need to use a properties file.

Merging YAML lists

As we have seen above, any YAML content is ultimately transformed to properties. That process may be counter intuitive when overriding “list” properties via a profile.

For example, assume a MyPojo object with name and description attributes that are null by default. Let’s expose a list of MyPojo from FooProperties:

@ConfigurationProperties("foo")
public class FooProperties {

	private final List<MyPojo> list = new ArrayList<>();

	public List<MyPojo> getList() {
		return this.list;
	}

}

Consider the following configuration:

foo:
  list:
    - name: my name
      description: my description
---
spring:
  profiles: dev
foo:
  list:
       - name: my another name

If the dev profile isn’t active, FooProperties.list will contain one MyPojo entry as defined above. If the dev profile is enabled however, the list will still only contain one entry (with name “my another name” and description null). This configuration will not add a second MyPojo instance to the list, and it won’t merge the items.

When a collection is specified in multiple profiles, the one with highest priority is used (and only that one):

foo:
  list:
	- name: my name
	  description: my description
	- name: another name
	  description: another description
---
spring:
  profiles: dev
foo:
  list:
	 - name: my another name

In the example above, considering that the dev profile is active, FooProperties.list will contain one MyPojo entry (with name “my another name” and description null).

Type-safe Configuration Properties

Using the @Value("${property}") annotation to inject configuration properties can sometimes be cumbersome, especially if you are working with multiple properties or your data is hierarchical in nature. Spring Boot provides an alternative method of working with properties that allows strongly typed beans to govern and validate the configuration of your application.

package com.example;

import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties("foo")
public class FooProperties {

	private boolean enabled;

	private InetAddress remoteAddress;

	private final Security security = new Security();

	public boolean isEnabled() { ... }

	public void setEnabled(boolean enabled) { ... }

	public InetAddress getRemoteAddress() { ... }

	public void setRemoteAddress(InetAddress remoteAddress) { ... }

	public Security getSecurity() { ... }

	public static class Security {

		private String username;

		private String password;

		private List<String> roles = new ArrayList<>(Collections.singleton("USER"));

		public String getUsername() { ... }

		public void setUsername(String username) { ... }

		public String getPassword() { ... }

		public void setPassword(String password) { ... }

		public List<String> getRoles() { ... }

		public void setRoles(List<String> roles) { ... }

	}
}

The POJO above defines the following properties:

• foo.enabled, false by default

• foo.remote-address, with a type that can be coerced from String

• foo.security.username, with a nested "security" whose name is determined by the name of the property. In particular the return type is not used at all there and could have been SecurityProperties

• foo.security.password

• foo.security.roles, with a collection of String

Note

Getters and setters are usually mandatory, since binding is via standard Java Beans property descriptors, just like in Spring MVC. There are cases where a setter may be omitted: Maps, as long as they are initialized, need a getter but not necessarily a setter since they can be mutated by the binder. Collections and arrays can be either accessed via an index (typically with YAML) or using a single comma-separated value (properties). In the latter case, a setter is mandatory. We recommend to always add a setter for such types. If you initialize a collection, make sure it is not immutable (as in the example above) If nested POJO properties are initialized (like the Security field in the example above), a setter is not required. If you want the binder to create the instance on-the-fly using its default constructor, you will need a setter. Some people use Project Lombok to add getters and setters automatically. Make sure that Lombok doesn’t generate any particular constructor for such type as it will be used automatically by the container to instantiate the object.

Tip	See also the differences between @Value and @ConfigurationProperties.

You also need to list the properties classes to register in the @EnableConfigurationProperties annotation:

@Configuration
@EnableConfigurationProperties(FooProperties.class)
public class MyConfiguration {
}

Note

When @ConfigurationProperties bean is registered that way, the bean will have a conventional name: <prefix>-<fqn>, where <prefix> is the environment key prefix specified in the @ConfigurationProperties annotation and <fqn> the fully qualified name of the bean. If the annotation does not provide any prefix, only the fully qualified name of the bean is used. The bean name in the example above will be foo-com.example.FooProperties.

Even if the configuration above will create a regular bean for FooProperties, we recommend that @ConfigurationProperties only deal with the environment and in particular does not inject other beans from the context. Having said that, The @EnableConfigurationProperties annotation is also automatically applied to your project so that any existing bean annotated with @ConfigurationProperties will be configured from the Environment. You could shortcut MyConfiguration above by making sure FooProperties is a already a bean:

@Component
@ConfigurationProperties(prefix="foo")
public class FooProperties {

	// ... see above

}

This style of configuration works particularly well with the SpringApplication external YAML configuration:

# application.yml

foo:
	remote-address: 192.168.1.1
	security:
		username: foo
		roles:
		  - USER
		  - ADMIN

# additional configuration as required

To work with @ConfigurationProperties beans you can just inject them in the same way as any other bean.

@Service
public class MyService {

	private final FooProperties properties;

	@Autowired
	public MyService(FooProperties properties) {
	    this.properties = properties;
	}

 	//...

	@PostConstruct
	public void openConnection() {
		Server server = new Server(this.properties.getRemoteAddress());
		// ...
	}

}

Tip	Using @ConfigurationProperties also allows you to generate meta-data files that can be used by IDEs to offer auto-completion for your own keys, see the [configuration-metadata] appendix for details.

Third-party configuration

As well as using @ConfigurationProperties to annotate a class, you can also use it on public @Bean methods. This can be particularly useful when you want to bind properties to third-party components that are outside of your control.

To configure a bean from the Environment properties, add @ConfigurationProperties to its bean registration:

@ConfigurationProperties(prefix = "bar")
@Bean
public BarComponent barComponent() {
	...
}

Any property defined with the bar prefix will be mapped onto that BarComponent bean in a similar manner as the FooProperties example above.

Relaxed binding

Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, so there doesn’t need to be an exact match between the Environment property name and the bean property name. Common examples where this is useful include dashed separated (e.g. context-path binds to contextPath), and capitalized (e.g. PORT binds to port) environment properties.

For example, given the following @ConfigurationProperties class:

@ConfigurationProperties(prefix="person")
public class OwnerProperties {

	private String firstName;

	public String getFirstName() {
		return this.firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

}

The following properties names can all be used:

Table 2. relaxed binding

Property	Note
person.firstName	Standard camel case syntax.
person.first-name	Dashed notation, recommended for use in .properties and .yml files.
person.first_name	Underscore notation, alternative format for use in .properties and .yml files.
PERSON_FIRST_NAME	Upper case format. Recommended when using a system environment variables.

Properties conversion

Spring will attempt to coerce the external application properties to the right type when it binds to the @ConfigurationProperties beans. If you need custom type conversion you can provide a ConversionService bean (with bean id conversionService) or custom property editors (via a CustomEditorConfigurer bean) or custom Converters (with bean definitions annotated as @ConfigurationPropertiesBinding).

Note

As this bean is requested very early during the application lifecycle, make sure to limit the dependencies that your ConversionService is using. Typically, any dependency that you require may not be fully initialized at creation time. You may want to rename your custom ConversionService if it’s not required for configuration keys coercion and only rely on custom converters qualified with @ConfigurationPropertiesBinding.

@ConfigurationProperties Validation

Spring Boot will attempt to validate @ConfigurationProperties classes whenever they are annotated with Spring’s @Validated annotation. You can use JSR-303 javax.validation constraint annotations directly on your configuration class. Simply ensure that a compliant JSR-303 implementation is on your classpath, then add constraint annotations to your fields:

@ConfigurationProperties(prefix="foo")
@Validated
public class FooProperties {

	@NotNull
	private InetAddress remoteAddress;

	// ... getters and setters

}

In order to validate values of nested properties, you must annotate the associated field as @Valid to trigger its validation. For example, building upon the above FooProperties example:

@ConfigurationProperties(prefix="connection")
@Validated
public class FooProperties {

	@NotNull
	private InetAddress remoteAddress;

	@Valid
	private final Security security = new Security();

	// ... getters and setters

	public static class Security {

		@NotEmpty
		public String username;

		// ... getters and setters

	}

}

You can also add a custom Spring Validator by creating a bean definition called configurationPropertiesValidator. The @Bean method should be declared static. The configuration properties validator is created very early in the application’s lifecycle and declaring the @Bean method as static allows the bean to be created without having to instantiate the @Configuration class. This avoids any problems that may be caused by early instantiation. There is a {github-code}/spring-boot-samples/spring-boot-sample-property-validation[property validation sample] so you can see how to set things up.

Tip	The spring-boot-actuator module includes an endpoint that exposes all @ConfigurationProperties beans. Simply point your web browser to /configprops or use the equivalent JMX endpoint. See the Production ready features. section for details.

@ConfigurationProperties vs. @Value

@Value is a core container feature and it does not provide the same features as type-safe Configuration Properties. The table below summarizes the features that are supported by @ConfigurationProperties and @Value:

Feature	@ConfigurationProperties	@Value
Relaxed binding	Yes	No
Meta-data support	Yes	No
SpEL evaluation	No	Yes

If you define a set of configuration keys for your own components, we recommend you to group them in a POJO annotated with @ConfigurationProperties. Please also be aware that since @Value does not support relaxed binding, it isn’t a great candidate if you need to provide the value using environment variables.

Finally, while you can write a SpEL expression in @Value, such expressions are not processed from Application property files.

Profiles

Spring Profiles provide a way to segregate parts of your application configuration and make it only available in certain environments. Any @Component or @Configuration can be marked with @Profile to limit when it is loaded:

@Configuration
@Profile("production")
public class ProductionConfiguration {

	// ...

}

In the normal Spring way, you can use a spring.profiles.active Environment property to specify which profiles are active. You can specify the property in any of the usual ways, for example you could include it in your application.properties:

spring.profiles.active=dev,hsqldb

or specify on the command line using the switch --spring.profiles.active=dev,hsqldb.

Adding active profiles

The spring.profiles.active property follows the same ordering rules as other properties, the highest PropertySource will win. This means that you can specify active profiles in application.properties then replace them using the command line switch.

Sometimes it is useful to have profile-specific properties that add to the active profiles rather than replace them. The spring.profiles.include property can be used to unconditionally add active profiles. The SpringApplication entry point also has a Java API for setting additional profiles (i.e. on top of those activated by the spring.profiles.active property): see the setAdditionalProfiles() method.

For example, when an application with following properties is run using the switch --spring.profiles.active=prod the proddb and prodmq profiles will also be activated:

---
my.property: fromyamlfile
---
spring.profiles: prod
spring.profiles.include:
  - proddb
  - prodmq

Note	Remember that the spring.profiles property can be defined in a YAML document to determine when this particular document is included in the configuration. See [howto-change-configuration-depending-on-the-environment] for more details.

Programmatically setting profiles

You can programmatically set active profiles by calling SpringApplication.setAdditionalProfiles(…​) before your application runs. It is also possible to activate profiles using Spring’s ConfigurableEnvironment interface.

Profile-specific configuration files

Profile-specific variants of both application.properties (or application.yml) and files referenced via @ConfigurationProperties are considered as files are loaded. See Profile-specific properties for details.

Logging

Spring Boot uses Commons Logging for all internal logging, but leaves the underlying log implementation open. Default configurations are provided for Java Util Logging, Log4J2 and Logback. In each case loggers are pre-configured to use console output with optional file output also available.

By default, If you use the ‘Starters’, Logback will be used for logging. Appropriate Logback routing is also included to ensure that dependent libraries that use Java Util Logging, Commons Logging, Log4J or SLF4J will all work correctly.

Tip	There are a lot of logging frameworks available for Java. Don’t worry if the above list seems confusing. Generally you won’t need to change your logging dependencies and the Spring Boot defaults will work just fine.

Log format

The default log output from Spring Boot looks like this:

2014-03-05 10:57:51.112  INFO 45469 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/7.0.52
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1358 ms
2014-03-05 10:57:51.698  INFO 45469 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean        : Mapping servlet: 'dispatcherServlet' to [/]
2014-03-05 10:57:51.702  INFO 45469 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]

The following items are output:

• Date and Time — Millisecond precision and easily sortable.

• Log Level — ERROR, WARN, INFO, DEBUG or TRACE.

• Process ID.

• A --- separator to distinguish the start of actual log messages.

• Thread name — Enclosed in square brackets (may be truncated for console output).

• Logger name — This is usually the source class name (often abbreviated).

• The log message.

Note	Logback does not have a FATAL level (it is mapped to ERROR)

Console output

The default log configuration will echo messages to the console as they are written. By default ERROR, WARN and INFO level messages are logged. You can also enable a “debug” mode by starting your application with a --debug flag.

$ java -jar myapp.jar --debug

Note	you can also specify debug=true in your application.properties.

When the debug mode is enabled, a selection of core loggers (embedded container, Hibernate and Spring Boot) are configured to output more information. Enabling the debug mode does not configure your application to log all messages with DEBUG level.

Alternatively, you can enable a “trace” mode by starting your application with a --trace flag (or trace=true in your application.properties). This will enable trace logging for a selection of core loggers (embedded container, Hibernate schema generation and the whole Spring portfolio).

Color-coded output

If your terminal supports ANSI, color output will be used to aid readability. You can set spring.output.ansi.enabled to a {dc-spring-boot}/ansi/AnsiOutput.Enabled.{dc-ext}[supported value] to override the auto detection.

Color coding is configured using the %clr conversion word. In its simplest form the converter will color the output according to the log level, for example:

%clr(%5p)

The mapping of log level to a color is as follows:

Level	Color
FATAL	Red
ERROR	Red
WARN	Yellow
INFO	Green
DEBUG	Green
TRACE	Green

Alternatively, you can specify the color or style that should be used by providing it as an option to the conversion. For example, to make the text yellow:

%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){yellow}

The following colors and styles are supported:

• blue

• cyan

• faint

• green

• magenta

• red

• yellow

File output

By default, Spring Boot will only log to the console and will not write log files. If you want to write log files in addition to the console output you need to set a logging.file or logging.path property (for example in your application.properties).

The following table shows how the logging.* properties can be used together:

Table 3. Logging properties

logging.file	logging.path	Example	Description
(none)	(none)		Console only logging.
Specific file	(none)	my.log	Writes to the specified log file. Names can be an exact location or relative to the current directory.
(none)	Specific directory	/var/log	Writes spring.log to the specified directory. Names can be an exact location or relative to the current directory.

Log files will rotate when they reach 10 MB and as with console output, ERROR, WARN and INFO level messages are logged by default.

Note	The logging system is initialized early in the application lifecycle and as such logging properties will not be found in property files loaded via @PropertySource annotations.

Tip	Logging properties are independent of the actual logging infrastructure. As a result, specific configuration keys (such as logback.configurationFile for Logback) are not managed by spring Boot.

Log Levels

All the supported logging systems can have the logger levels set in the Spring Environment (so for example in application.properties) using ‘logging.level.*=LEVEL’ where ‘LEVEL’ is one of TRACE, DEBUG, INFO, WARN, ERROR, FATAL, OFF. The root logger can be configured using logging.level.root. Example application.properties:

logging.level.root=WARN
logging.level.org.springframework.web=DEBUG
logging.level.org.hibernate=ERROR

Note

By default Spring Boot remaps Thymeleaf INFO messages so that they are logged at DEBUG level. This helps to reduce noise in the standard log output. See {sc-spring-boot}/logging/logback/LevelRemappingAppender.{sc-ext}[LevelRemappingAppender] for details of how you can apply remapping in your own configuration.

Custom log configuration

The various logging systems can be activated by including the appropriate libraries on the classpath, and further customized by providing a suitable configuration file in the root of the classpath, or in a location specified by the Spring Environment property logging.config.

You can force Spring Boot to use a particular logging system using the org.springframework.boot.logging.LoggingSystem system property. The value should be the fully-qualified class name of a LoggingSystem implementation. You can also disable Spring Boot’s logging configuration entirely by using a value of none.

Note	Since logging is initialized before the ApplicationContext is created, it isn’t possible to control logging from @PropertySources in Spring @Configuration files. System properties and the conventional Spring Boot external configuration files work just fine.)

Depending on your logging system, the following files will be loaded:

Logging System	Customization
Logback	logback-spring.xml, logback-spring.groovy, logback.xml or logback.groovy
Log4j2	log4j2-spring.xml or log4j2.xml
JDK (Java Util Logging)	logging.properties

Note	When possible we recommend that you use the -spring variants for your logging configuration (for example logback-spring.xml rather than logback.xml). If you use standard configuration locations, Spring cannot completely control log initialization.

Warning

There are known classloading issues with Java Util Logging that cause problems when running from an ‘executable jar’. We recommend that you avoid it if at all possible.

To help with the customization some other properties are transferred from the Spring Environment to System properties:

Spring Environment	System Property	Comments
logging.exception-conversion-word	LOG_EXCEPTION_CONVERSION_WORD	The conversion word that’s used when logging exceptions.
logging.file	LOG_FILE	Used in default log configuration if defined.
logging.path	LOG_PATH	Used in default log configuration if defined.
logging.pattern.console	CONSOLE_LOG_PATTERN	The log pattern to use on the console (stdout). (Only supported with the default logback setup.)
logging.pattern.file	FILE_LOG_PATTERN	The log pattern to use in a file (if LOG_FILE enabled). (Only supported with the default logback setup.)
logging.pattern.level	LOG_LEVEL_PATTERN	The format to use to render the log level (default %5p). (Only supported with the default logback setup.)
PID	PID	The current process ID (discovered if possible and when not already defined as an OS environment variable).

All the logging systems supported can consult System properties when parsing their configuration files. See the default configurations in spring-boot.jar for examples.

Tip	If you want to use a placeholder in a logging property, you should use Spring Boot’s syntax and not the syntax of the underlying framework. Notably, if you’re using Logback, you should use : as the delimiter between a property name and its default value and not :-.

Tip

You can add MDC and other ad-hoc content to log lines by overriding only the LOG_LEVEL_PATTERN (or logging.pattern.level with Logback). For example, if you use logging.pattern.level=user:%X{user} %5p then the default log format will contain an MDC entry for "user" if it exists, e.g. 2015-09-30 12:30:04.031 user:juergen INFO 22174 --- [ nio-8080-exec-0] demo.Controller Handling authenticated request

Logback extensions

Spring Boot includes a number of extensions to Logback which can help with advanced configuration. You can use these extensions in your logback-spring.xml configuration file.

Note	You cannot use extensions in the standard logback.xml configuration file since it’s loaded too early. You need to either use logback-spring.xml or define a logging.config property.

Warning

The extensions cannot be used with Logback’s configuration scanning. If you attempt to do so, making changes to the configuration file will result in an error similar to one of the following being logged:

ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProperty], current ElementPath is [[configuration][springProperty]]
ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProfile], current ElementPath is [[configuration][springProfile]]

Profile-specific configuration

The <springProfile> tag allows you to optionally include or exclude sections of configuration based on the active Spring profiles. Profile sections are supported anywhere within the <configuration> element. Use the name attribute to specify which profile accepts the configuration. Multiple profiles can be specified using a comma-separated list.

<springProfile name="staging">
	<!-- configuration to be enabled when the "staging" profile is active -->
</springProfile>

<springProfile name="dev, staging">
	<!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
</springProfile>

<springProfile name="!production">
	<!-- configuration to be enabled when the "production" profile is not active -->
</springProfile>

Environment properties

The <springProperty> tag allows you to surface properties from the Spring Environment for use within Logback. This can be useful if you want to access values from your application.properties file in your logback configuration. The tag works in a similar way to Logback’s standard <property> tag, but rather than specifying a direct value you specify the source of the property (from the Environment). You can use the scope attribute if you need to store the property somewhere other than in local scope. If you need a fallback value in case the property is not set in the Environment, you can use the defaultValue attribute.

<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"
		defaultValue="localhost"/>
<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
	<remoteHost>${fluentHost}</remoteHost>
	...
</appender>

Tip	The RelaxedPropertyResolver is used to access Environment properties. If specify the source in dashed notation (my-property-name) all the relaxed variations will be tried (myPropertyName, MY_PROPERTY_NAME etc).

Developing web applications

Spring Boot is well suited for web application development. You can easily create a self-contained HTTP server using embedded Tomcat, Jetty, or Undertow. Most web applications will use the spring-boot-starter-web module to get up and running quickly.

If you haven’t yet developed a Spring Boot web application you can follow the "Hello World!" example in the Getting started section.

The ‘Spring Web MVC framework’

The Spring Web MVC framework (often referred to as simply ‘Spring MVC’) is a rich ‘model view controller’ web framework. Spring MVC lets you create special @Controller or @RestController beans to handle incoming HTTP requests. Methods in your controller are mapped to HTTP using @RequestMapping annotations.

Here is a typical example @RestController to serve JSON data:

@RestController
@RequestMapping(value="/users")
public class MyRestController {

	@RequestMapping(value="/{user}", method=RequestMethod.GET)
	public User getUser(@PathVariable Long user) {
		// ...
	}

	@RequestMapping(value="/{user}/customers", method=RequestMethod.GET)
	List<Customer> getUserCustomers(@PathVariable Long user) {
		// ...
	}

	@RequestMapping(value="/{user}", method=RequestMethod.DELETE)
	public User deleteUser(@PathVariable Long user) {
		// ...
	}

}

Spring MVC is part of the core Spring Framework and detailed information is available in the {spring-reference}#mvc[reference documentation]. There are also several guides available at http://spring.io/guides that cover Spring MVC.

Spring MVC auto-configuration

Spring Boot provides auto-configuration for Spring MVC that works well with most applications.

The auto-configuration adds the following features on top of Spring’s defaults:

• Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans.

• Support for serving static resources, including support for WebJars (see below).

• Automatic registration of Converter, GenericConverter, Formatter beans.

• Support for HttpMessageConverters (see below).

• Automatic registration of MessageCodesResolver (see below).

• Static index.html support.

• Custom Favicon support (see below).

• Automatic use of a ConfigurableWebBindingInitializer bean (see below).

If you want to keep Spring Boot MVC features, and you just want to add additional {spring-reference}#mvc[MVC configuration] (interceptors, formatters, view controllers etc.) you can add your own @Configuration class of type WebMvcConfigurerAdapter, but without @EnableWebMvc. If you wish to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter or ExceptionHandlerExceptionResolver you can declare a WebMvcRegistrationsAdapter instance providing such components.

If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc.

HttpMessageConverters

Spring MVC uses the HttpMessageConverter interface to convert HTTP requests and responses. Sensible defaults are included out of the box, for example Objects can be automatically converted to JSON (using the Jackson library) or XML (using the Jackson XML extension if available, else using JAXB). Strings are encoded using UTF-8 by default.

If you need to add or customize converters you can use Spring Boot’s HttpMessageConverters class:

import org.springframework.boot.autoconfigure.web.HttpMessageConverters;
import org.springframework.context.annotation.*;
import org.springframework.http.converter.*;

@Configuration
public class MyConfiguration {

	@Bean
	public HttpMessageConverters customConverters() {
		HttpMessageConverter<?> additional = ...
		HttpMessageConverter<?> another = ...
		return new HttpMessageConverters(additional, another);
	}

}

Any HttpMessageConverter bean that is present in the context will be added to the list of converters. You can also override default converters that way.

Custom JSON Serializers and Deserializers

If you’re using Jackson to serialize and deserialize JSON data, you might want to write your own JsonSerializer and JsonDeserializer classes. Custom serializers are usually registered with Jackson via a Module, but Spring Boot provides an alternative @JsonComponent annotation which makes it easier to directly register Spring Beans.

You can use @JsonComponent directly on JsonSerializer or JsonDeserializer implementations. You can also use it on classes that contains serializers/deserializers as inner-classes. For example:

import java.io.*;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.*;
import org.springframework.boot.jackson.*;

@JsonComponent
public class Example {

	public static class Serializer extends JsonSerializer<SomeObject> {
		// ...
	}

	public static class Deserializer extends JsonDeserializer<SomeObject> {
		// ...
	}

}

All @JsonComponent beans in the ApplicationContext will be automatically registered with Jackson, and since @JsonComponent is meta-annotated with @Component, the usual component-scanning rules apply.

Spring Boot also provides {sc-spring-boot}/jackson/JsonObjectSerializer.{sc-ext}[JsonObjectSerializer] and {sc-spring-boot}/jackson/JsonObjectDeserializer.{sc-ext}[JsonObjectDeserializer] base classes which provide useful alternatives to the standard Jackson versions when serializing Objects. See the Javadoc for details.

MessageCodesResolver

Spring MVC has a strategy for generating error codes for rendering error messages from binding errors: MessageCodesResolver. Spring Boot will create one for you if you set the spring.mvc.message-codes-resolver.format property PREFIX_ERROR_CODE or POSTFIX_ERROR_CODE (see the enumeration in DefaultMessageCodesResolver.Format).

Static Content

By default Spring Boot will serve static content from a directory called /static (or /public or /resources or /META-INF/resources) in the classpath or from the root of the ServletContext. It uses the ResourceHttpRequestHandler from Spring MVC so you can modify that behavior by adding your own WebMvcConfigurerAdapter and overriding the addResourceHandlers method.

In a stand-alone web application the default servlet from the container is also enabled, and acts as a fallback, serving content from the root of the ServletContext if Spring decides not to handle it. Most of the time this will not happen (unless you modify the default MVC configuration) because Spring will always be able to handle requests through the DispatcherServlet.

By default, resources are mapped on /** but you can tune that via spring.mvc.static-path-pattern. For instance, relocating all resources to /resources/** can be achieved as follows:

spring.mvc.static-path-pattern=/resources/**

You can also customize the static resource locations using spring.resources.static-locations (replacing the default values with a list of directory locations). If you do this the default welcome page detection will switch to your custom locations, so if there is an index.html in any of your locations on startup, it will be the home page of the application.

In addition to the ‘standard’ static resource locations above, a special case is made for Webjars content. Any resources with a path in /webjars/** will be served from jar files if they are packaged in the Webjars format.

Tip	Do not use the src/main/webapp directory if your application will be packaged as a jar. Although this directory is a common standard, it will only work with war packaging and it will be silently ignored by most build tools if you generate a jar.

Spring Boot also supports advanced resource handling features provided by Spring MVC, allowing use cases such as cache busting static resources or using version agnostic URLs for Webjars.

To use version agnostic URLs for Webjars, simply add the webjars-locator dependency. Then declare your Webjar, taking jQuery for example, as "/webjars/jquery/dist/jquery.min.js" which results in "/webjars/jquery/x.y.z/dist/jquery.min.js" where x.y.z is the Webjar version.

Note	If you are using JBoss, you’ll need to declare the webjars-locator-jboss-vfs dependency instead of the webjars-locator; otherwise all Webjars resolve as a 404.

To use cache busting, the following configuration will configure a cache busting solution for all static resources, effectively adding a content hash in URLs, such as <link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>:

spring.resources.chain.strategy.content.enabled=true
spring.resources.chain.strategy.content.paths=/**

Note

Links to resources are rewritten at runtime in template, thanks to a ResourceUrlEncodingFilter, auto-configured for Thymeleaf and FreeMarker. You should manually declare this filter when using JSPs. Other template engines aren’t automatically supported right now, but can be with custom template macros/helpers and the use of the {spring-javadoc}/web/servlet/resource/ResourceUrlProvider.{dc-ext}[ResourceUrlProvider].

When loading resources dynamically with, for example, a JavaScript module loader, renaming files is not an option. That’s why other strategies are also supported and can be combined. A "fixed" strategy will add a static version string in the URL, without changing the file name:

spring.resources.chain.strategy.content.enabled=true
spring.resources.chain.strategy.content.paths=/**
spring.resources.chain.strategy.fixed.enabled=true
spring.resources.chain.strategy.fixed.paths=/js/lib/
spring.resources.chain.strategy.fixed.version=v12

With this configuration, JavaScript modules located under "/js/lib/" will use a fixed versioning strategy "/v12/js/lib/mymodule.js" while other resources will still use the content one <link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>.

See {sc-spring-boot-autoconfigure}/web/ResourceProperties.{sc-ext}[ResourceProperties] for more of the supported options.

Tip	This feature has been thoroughly described in a dedicated blog post and in Spring Framework’s {spring-reference}/#mvc-config-static-resources[reference documentation].

Custom Favicon

Spring Boot looks for a favicon.ico in the configured static content locations and the root of the classpath (in that order). If such file is present, it is automatically used as the favicon of the application.

ConfigurableWebBindingInitializer

Spring MVC uses a WebBindingInitializer to initialize a WebDataBinder for a particular request. If you create your own ConfigurableWebBindingInitializer @Bean, Spring Boot will automatically configure Spring MVC to use it.

Template engines

As well as REST web services, you can also use Spring MVC to serve dynamic HTML content. Spring MVC supports a variety of templating technologies including Thymeleaf, FreeMarker and JSPs. Many other templating engines also ship their own Spring MVC integrations.

Spring Boot includes auto-configuration support for the following templating engines:

• FreeMarker

• Groovy

• Thymeleaf

• Mustache

Tip	JSPs should be avoided if possible, there are several known limitations when using them with embedded servlet containers.

When you’re using one of these templating engines with the default configuration, your templates will be picked up automatically from src/main/resources/templates.

Tip

IntelliJ IDEA orders the classpath differently depending on how you run your application. Running your application in the IDE via its main method will result in a different ordering to when you run your application using Maven or Gradle or from its packaged jar. This can cause Spring Boot to fail to find the templates on the classpath. If you’re affected by this problem you can reorder the classpath in the IDE to place the module’s classes and resources first. Alternatively, you can configure the template prefix to search every templates directory on the classpath: classpath*:/templates/.

Error Handling

Spring Boot provides an /error mapping by default that handles all errors in a sensible way, and it is registered as a ‘global’ error page in the servlet container. For machine clients it will produce a JSON response with details of the error, the HTTP status and the exception message. For browser clients there is a ‘whitelabel’ error view that renders the same data in HTML format (to customize it just add a View that resolves to ‘error’). To replace the default behaviour completely you can implement ErrorController and register a bean definition of that type, or simply add a bean of type ErrorAttributes to use the existing mechanism but replace the contents.

Tip

The BasicErrorController can be used as a base class for a custom ErrorController. This is particularly useful if you want to add a handler for a new content type (the default is to handle text/html specifically and provide a fallback for everything else). To do that just extend BasicErrorController and add a public method with a @RequestMapping that has a produces attribute, and create a bean of your new type.

You can also define a @ControllerAdvice to customize the JSON document to return for a particular controller and/or exception type.

@ControllerAdvice(basePackageClasses = FooController.class)
public class FooControllerAdvice extends ResponseEntityExceptionHandler {

	@ExceptionHandler(YourException.class)
	@ResponseBody
	ResponseEntity<?> handleControllerException(HttpServletRequest request, Throwable ex) {
		HttpStatus status = getStatus(request);
		return new ResponseEntity<>(new CustomErrorType(status.value(), ex.getMessage()), status);
	}

	private HttpStatus getStatus(HttpServletRequest request) {
		Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
		if (statusCode == null) {
			return HttpStatus.INTERNAL_SERVER_ERROR;
		}
		return HttpStatus.valueOf(statusCode);
	}

}

In the example above, if YourException is thrown by a controller defined in the same package as FooController, a json representation of the CustomerErrorType POJO will be used instead of the ErrorAttributes representation.

Custom error pages

If you want to display a custom HTML error page for a given status code, you add a file to an /error folder. Error pages can either be static HTML (i.e. added under any of the static resource folders) or built using templates. The name of the file should be the exact status code or a series mask.

For example, to map 404 to a static HTML file, your folder structure would look like this:

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- public/
             +- error/
             |   +- 404.html
             +- <other public assets>

To map all 5xx errors using a FreeMarker template, you’d have a structure like this:

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- templates/
             +- error/
             |   +- 5xx.ftl
             +- <other templates>

For more complex mappings you can also add beans that implement the ErrorViewResolver interface.

public class MyErrorViewResolver implements ErrorViewResolver {

	@Override
	public ModelAndView resolveErrorView(HttpServletRequest request,
			HttpStatus status, Map<String, Object> model) {
		// Use the request or status to optionally return a ModelAndView
		return ...
	}

}

You can also use regular Spring MVC features like {spring-reference}/#mvc-exceptionhandlers[@ExceptionHandler methods] and {spring-reference}/#mvc-ann-controller-advice[@ControllerAdvice]. The ErrorController will then pick up any unhandled exceptions.

Mapping error pages outside of Spring MVC

For applications that aren’t using Spring MVC, you can use the ErrorPageRegistrar interface to directly register ErrorPages. This abstraction works directly with the underlying embedded servlet container and will work even if you don’t have a Spring MVC DispatcherServlet.

@Bean
public ErrorPageRegistrar errorPageRegistrar(){
	return new MyErrorPageRegistrar();
}

// ...

private static class MyErrorPageRegistrar implements ErrorPageRegistrar {

	@Override
	public void registerErrorPages(ErrorPageRegistry registry) {
		registry.addErrorPages(new ErrorPage(HttpStatus.BAD_REQUEST, "/400"));
	}

}

N.B. if you register an ErrorPage with a path that will end up being handled by a Filter (e.g. as is common with some non-Spring web frameworks, like Jersey and Wicket), then the Filter has to be explicitly registered as an ERROR dispatcher, e.g.

@Bean
public FilterRegistrationBean myFilter() {
	FilterRegistrationBean registration = new FilterRegistrationBean();
	registration.setFilter(new MyFilter());
	...
	registration.setDispatcherTypes(EnumSet.allOf(DispatcherType.class));
	return registration;
}

(the default FilterRegistrationBean does not include the ERROR dispatcher type).

Error Handling on WebSphere Application Server

When deployed to a servlet container, a Spring Boot uses its error page filter to forward a request with an error status to the appropriate error page. The request can only be forwarded to the correct error page if the response has not already been committed. By default, WebSphere Application Server 8.0 and later commits the response upon successful completion of a servlet’s service method. You should disable this behaviour by setting com.ibm.ws.webcontainer.invokeFlushAfterService to false

Spring HATEOAS

If you’re developing a RESTful API that makes use of hypermedia, Spring Boot provides auto-configuration for Spring HATEOAS that works well with most applications. The auto-configuration replaces the need to use @EnableHypermediaSupport and registers a number of beans to ease building hypermedia-based applications including a LinkDiscoverers (for client side support) and an ObjectMapper configured to correctly marshal responses into the desired representation. The ObjectMapper will be customized based on the spring.jackson.* properties or a Jackson2ObjectMapperBuilder bean if one exists.

You can take control of Spring HATEOAS’s configuration by using @EnableHypermediaSupport. Note that this will disable the ObjectMapper customization described above.

CORS support

Cross-origin resource sharing (CORS) is a W3C specification implemented by most browsers that allows you to specify in a flexible way what kind of cross domain requests are authorized, instead of using some less secure and less powerful approaches like IFRAME or JSONP.

As of version 4.2, Spring MVC {spring-reference}/#cors[supports CORS] out of the box. Using {spring-reference}/#_controller_method_cors_configuration[controller method CORS configuration] with {spring-javadoc}/web/bind/annotation/CrossOrigin.html[@CrossOrigin] annotations in your Spring Boot application does not require any specific configuration. {spring-reference}/#_global_cors_configuration[Global CORS configuration] can be defined by registering a WebMvcConfigurer bean with a customized addCorsMappings(CorsRegistry) method:

@Configuration
public class MyConfiguration {

	@Bean
	public WebMvcConfigurer corsConfigurer() {
		return new WebMvcConfigurerAdapter() {
			@Override
			public void addCorsMappings(CorsRegistry registry) {
				registry.addMapping("/api/**");
			}
		};
	}
}

JAX-RS and Jersey

If you prefer the JAX-RS programming model for REST endpoints you can use one of the available implementations instead of Spring MVC. Jersey 1.x and Apache CXF work quite well out of the box if you just register their Servlet or Filter as a @Bean in your application context. Jersey 2.x has some native Spring support so we also provide auto-configuration support for it in Spring Boot together with a starter.

To get started with Jersey 2.x just include the spring-boot-starter-jersey as a dependency and then you need one @Bean of type ResourceConfig in which you register all the endpoints:

@Component
public class JerseyConfig extends ResourceConfig {

	public JerseyConfig() {
		register(Endpoint.class);
	}

}

Warning

Jersey’s support for scanning executable archives is rather limited. For example, it cannot scan for endpoints in a package found in WEB-INF/classes when running an executable war file. To avoid this limitation, the packages method should not be used and endpoints should be registered individually using the register method as shown above.

You can also register an arbitrary number of beans implementing ResourceConfigCustomizer for more advanced customizations.

All the registered endpoints should be @Components with HTTP resource annotations (@GET etc.), e.g.

@Component
@Path("/hello")
public class Endpoint {

	@GET
	public String message() {
		return "Hello";
	}

}

Since the Endpoint is a Spring @Component its lifecycle is managed by Spring and you can @Autowired dependencies and inject external configuration with @Value. The Jersey servlet will be registered and mapped to /* by default. You can change the mapping by adding @ApplicationPath to your ResourceConfig.

By default Jersey will be set up as a Servlet in a @Bean of type ServletRegistrationBean named jerseyServletRegistration. By default, the servlet will be initialized lazily but you can customize it with spring.jersey.servlet.load-on-startup .You can disable or override that bean by creating one of your own with the same name. You can also use a Filter instead of a Servlet by setting spring.jersey.type=filter (in which case the @Bean to replace or override is jerseyFilterRegistration). The servlet has an @Order which you can set with spring.jersey.filter.order. Both the Servlet and the Filter registrations can be given init parameters using spring.jersey.init.* to specify a map of properties.

There is a {github-code}/spring-boot-samples/spring-boot-sample-jersey[Jersey sample] so you can see how to set things up. There is also a {github-code}/spring-boot-samples/spring-boot-sample-jersey1[Jersey 1.x sample]. Note that in the Jersey 1.x sample that the spring-boot maven plugin has been configured to unpack some Jersey jars so they can be scanned by the JAX-RS implementation (because the sample asks for them to be scanned in its Filter registration). You may need to do the same if any of your JAX-RS resources are packaged as nested jars.

Embedded servlet container support

Spring Boot includes support for embedded Tomcat, Jetty, and Undertow servers. Most developers will simply use the appropriate ‘Starter’ to obtain a fully configured instance. By default the embedded server will listen for HTTP requests on port 8080.

Warning

If you choose to use Tomcat on CentOS be aware that, by default, a temporary directory is used to store compiled JSPs, file uploads etc. This directory may be deleted by tmpwatch while your application is running leading to failures. To avoid this, you may want to customize your tmpwatch configuration so that tomcat.* directories are not deleted, or configure server.tomcat.basedir so that embedded Tomcat uses a different location.

Servlets, Filters, and listeners

When using an embedded servlet container you can register Servlets, Filters and all the listeners from the Servlet spec (e.g. HttpSessionListener) either by using Spring beans or by scanning for Servlet components.

Registering Servlets, Filters, and listeners as Spring beans

Any Servlet, Filter or Servlet *Listener instance that is a Spring bean will be registered with the embedded container. This can be particularly convenient if you want to refer to a value from your application.properties during configuration.

By default, if the context contains only a single Servlet it will be mapped to /. In the case of multiple Servlet beans the bean name will be used as a path prefix. Filters will map to /*.

If convention-based mapping is not flexible enough you can use the ServletRegistrationBean, FilterRegistrationBean and ServletListenerRegistrationBean classes for complete control.

Servlet Context Initialization

Embedded servlet containers will not directly execute the Servlet 3.0+ javax.servlet.ServletContainerInitializer interface, or Spring’s org.springframework.web.WebApplicationInitializer interface. This is an intentional design decision intended to reduce the risk that 3rd party libraries designed to run inside a war will break Spring Boot applications.

If you need to perform servlet context initialization in a Spring Boot application, you should register a bean that implements the org.springframework.boot.web.servlet.ServletContextInitializer interface. The single onStartup method provides access to the ServletContext, and can easily be used as an adapter to an existing WebApplicationInitializer if necessary.

Scanning for Servlets, Filters, and listeners

When using an embedded container, automatic registration of @WebServlet, @WebFilter, and @WebListener annotated classes can be enabled using @ServletComponentScan.

Tip	@ServletComponentScan will have no effect in a standalone container, where the container’s built-in discovery mechanisms will be used instead.

The ServletWebServerApplicationContext

Under the hood Spring Boot uses a new type of ApplicationContext for embedded servlet container support. The ServletWebServerApplicationContext is a special type of WebApplicationContext that bootstraps itself by searching for a single ServletWebServerFactory bean. Usually a TomcatServletWebServerFactory, JettyServletWebServerFactory, or UndertowServletWebServerFactory will have been auto-configured.

Note	You usually won’t need to be aware of these implementation classes. Most applications will be auto-configured and the appropriate ApplicationContext and ServletWebServerFactory will be created on your behalf.

Customizing embedded servlet containers

Common servlet container settings can be configured using Spring Environment properties. Usually you would define the properties in your application.properties file.

Common server settings include:

• Network settings: listen port for incoming HTTP requests (server.port), interface address to bind to server.address, etc.

• Session settings: whether the session is persistent (server.session.persistence), session timeout (server.session.timeout), location of session data (server.session.store-dir) and session-cookie configuration (server.session.cookie.*).

• Error management: location of the error page (server.error.path), etc.

• SSL

• HTTP compression

Spring Boot tries as much as possible to expose common settings but this is not always possible. For those cases, dedicated namespaces offer server-specific customizations (see server.tomcat and server.undertow). For instance, access logs can be configured with specific features of the embedded servlet container.

Tip	See the {sc-spring-boot-autoconfigure}/web/ServerProperties.{sc-ext}[ServerProperties] class for a complete list.

Programmatic customization

If you need to configure your embedded servlet container programmatically you can register a Spring bean that implements the WebServerFactoryCustomizer interface. WebServerFactoryCustomizer provides access to the ConfigurableServletWebServerFactory which includes numerous customization setter methods. Dedicated variants exists for Tomcat, Jetty and Undertow.

import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
import org.springframework.stereotype.Component;

@Component
public class CustomizationBean implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> {

	@Override
	public void customize(ConfigurableServletWebServerFactory server) {
		server.setPort(9000);
	}

}

Customizing ConfigurableServletWebServerFactory directly

If the above customization techniques are too limited, you can register the TomcatServletWebServerFactory, JettyServletWebServerFactory or UndertowServletWebServerFactory bean yourself.

@Bean
public ConfigurableServletWebServerFactory webServerFactory() {
	TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
	factory.setPort(9000);
	factory.setSessionTimeout(10, TimeUnit.MINUTES);
	factory.addErrorPages(new ErrorPage(HttpStatus.NOT_FOUND, "/notfound.html"));
	return factory;
}

Setters are provided for many configuration options. Several protected method ‘hooks’ are also provided should you need to do something more exotic. See the source code documentation for details.

JSP limitations

When running a Spring Boot application that uses an embedded servlet container (and is packaged as an executable archive), there are some limitations in the JSP support.

• With Tomcat it should work if you use war packaging, i.e. an executable war will work, and will also be deployable to a standard container (not limited to, but including Tomcat). An executable jar will not work because of a hard coded file pattern in Tomcat.

• With Jetty it should work if you use war packaging, i.e. an executable war will work, and will also be deployable to any standard container.

• Undertow does not support JSPs.

• Creating a custom error.jsp page won’t override the default view for error handling, custom error pages should be used instead.

There is a {github-code}/spring-boot-samples/spring-boot-sample-web-jsp[JSP sample] so you can see how to set things up.

Security

If Spring Security is on the classpath then web applications will be secure by default with ‘basic’ authentication on all HTTP endpoints. To add method-level security to a web application you can also add @EnableGlobalMethodSecurity with your desired settings. Additional information can be found in the {spring-security-reference}#jc-method[Spring Security Reference].

The default AuthenticationManager has a single user (‘user’ username and random password, printed at INFO level when the application starts up)

Using default security password: 78fa095d-3f4c-48b1-ad50-e24c31d5cf35

Note	If you fine-tune your logging configuration, ensure that the org.springframework.boot.autoconfigure.security category is set to log INFO messages, otherwise the default password will not be printed.

You can change the password by providing a security.user.password. This and other useful properties are externalized via {sc-spring-boot-autoconfigure}/security/SecurityProperties.{sc-ext}[SecurityProperties] (properties prefix "security").

The default security configuration is implemented in SecurityAutoConfiguration and in the classes imported from there (SpringBootWebSecurityConfiguration for web security and AuthenticationManagerConfiguration for authentication configuration which is also relevant in non-web applications). To switch off the default web application security configuration completely you can add a bean with @EnableWebSecurity (this does not disable the authentication manager configuration or Actuator’s security). To customize it you normally use external properties and beans of type WebSecurityConfigurerAdapter (e.g. to add form-based login). To also switch off the authentication manager configuration you can add a bean of type AuthenticationManager, or else configure the global AuthenticationManager by autowiring an AuthenticationManagerBuilder into a method in one of your @Configuration classes. There are several secure applications in the {github-code}/spring-boot-samples/[Spring Boot samples] to get you started with common use cases.

The basic features you get out of the box in a web application are:

• An AuthenticationManager bean with in-memory store and a single user (see SecurityProperties.User for the properties of the user).

• Ignored (insecure) paths for common static resource locations (/css/**, /js/**, /images/**, /webjars/** and **/favicon.ico).

• HTTP Basic security for all other endpoints.

• Security events published to Spring’s ApplicationEventPublisher (successful and unsuccessful authentication and access denied).

• Common low-level features (HSTS, XSS, CSRF, caching) provided by Spring Security are on by default.

All of the above can be switched on and off or modified using external properties (security.*). To override the access rules without changing any other auto-configured features add a @Bean of type WebSecurityConfigurerAdapter with @Order(SecurityProperties.ACCESS_OVERRIDE_ORDER) and configure it to meet your needs.

Note	By default, a WebSecurityConfigurerAdapter will match any path. If you don’t want to completely override Spring Boot’s auto-configured access rules, your adapter must explicitly configure the paths that you do want to override.

OAuth2

If you have spring-security-oauth2 on your classpath you can take advantage of some auto-configuration to make it easy to set up Authorization or Resource Server. For full details, see the {spring-security-oauth2-reference}[Spring Security OAuth 2 Developers Guide].

Authorization Server

To create an Authorization Server and grant access tokens you need to use @EnableAuthorizationServer and provide security.oauth2.client.client-id and security.oauth2.client.client-secret] properties. The client will be registered for you in an in-memory repository.

Having done that you will be able to use the client credentials to create an access token, for example:

$ curl client:secret@localhost:8080/oauth/token -d grant_type=password -d username=user -d password=pwd

The basic auth credentials for the /token endpoint are the client-id and client-secret. The user credentials are the normal Spring Security user details (which default in Spring Boot to “user” and a random password).

To switch off the auto-configuration and configure the Authorization Server features yourself just add a @Bean of type AuthorizationServerConfigurer.

Resource Server

To use the access token you need a Resource Server (which can be the same as the Authorization Server). Creating a Resource Server is easy, just add @EnableResourceServer and provide some configuration to allow the server to decode access tokens. If your application is also an Authorization Server it already knows how to decode tokens, so there is nothing else to do. If your app is a standalone service then you need to give it some more configuration, one of the following options:

• security.oauth2.resource.user-info-uri to use the /me resource (e.g. https://uaa.run.pivotal.io/userinfo on PWS)

• security.oauth2.resource.token-info-uri to use the token decoding endpoint (e.g. https://uaa.run.pivotal.io/check_token on PWS).

If you specify both the user-info-uri and the token-info-uri then you can set a flag to say that one is preferred over the other (prefer-token-info=true is the default).

Alternatively (instead of user-info-uri or token-info-uri) if the tokens are JWTs you can configure a security.oauth2.resource.jwt.key-value to decode them locally (where the key is a verification key). The verification key value is either a symmetric secret or PEM-encoded RSA public key. If you don’t have the key and it’s public you can provide a URI where it can be downloaded (as a JSON object with a “value” field) with security.oauth2.resource.jwt.key-uri. E.g. on PWS:

$ curl https://uaa.run.pivotal.io/token_key
{"alg":"SHA256withRSA","value":"-----BEGIN PUBLIC KEY-----\nMIIBI...\n-----END PUBLIC KEY-----\n"}

Warning

If you use the security.oauth2.resource.jwt.key-uri the authorization server needs to be running when your application starts up. It will log a warning if it can’t find the key, and tell you what to do to fix it.

OAuth2 resources are protected by a filter chain with order security.oauth2.resource.filter-order and the default is after the filter protecting the actuator endpoints by default (so actuator endpoints will stay on HTTP Basic unless you change the order).

Token Type in User Info

Google, and certain other 3rd party identity providers, are more strict about the token type name that is sent in the headers to the user info endpoint. The default is “Bearer” which suits most providers and matches the spec, but if you need to change it you can set security.oauth2.resource.token-type.

Customizing the User Info RestTemplate

If you have a user-info-uri, the resource server features use an OAuth2RestTemplate internally to fetch user details for authentication. This is provided as a @Bean of type UserInfoRestTemplateFactory. The default should be fine for most providers, but occasionally you might need to add additional interceptors, or change the request authenticator (which is how the token gets attached to outgoing requests). To add a customization just create a bean of type UserInfoRestTemplateCustomizer - it has a single method that will be called after the bean is created but before it is initialized. The rest template that is being customized here is only used internally to carry out authentication. Alternatively, you could define your own UserInfoRestTemplateFactory @Bean to take full control.

Tip

To set an RSA key value in YAML use the “pipe” continuation marker to split it over multiple lines (“|”) and remember to indent the key value (it’s a standard YAML language feature). Example: security: oauth2: resource: jwt: keyValue: | -----BEGIN PUBLIC KEY----- MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKC... -----END PUBLIC KEY-----

Client

To make your web-app into an OAuth2 client you can simply add @EnableOAuth2Client and Spring Boot will create a OAuth2ClientContext and OAuth2ProtectedResourceDetails that are necessary to create an OAuth2RestOperations. Spring Boot does not automatically create such bean but you can easily create your own:

@Bean
public OAuth2RestTemplate oauth2RestTemplate(OAuth2ClientContext oauth2ClientContext,
		OAuth2ProtectedResourceDetails details) {
	return new OAuth2RestTemplate(details, oauth2ClientContext);
}

Note	You may want to add a qualifier and review your configuration as more than one RestTemplate may be defined in your application.

This configuration uses security.oauth2.client.* as credentials (the same as you might be using in the Authorization Server), but in addition it will need to know the authorization and token URIs in the Authorization Server. For example:

application.yml

security:
	oauth2:
		client:
			clientId: bd1c0a783ccdd1c9b9e4
			clientSecret: 1a9030fbca47a5b2c28e92f19050bb77824b5ad1
			accessTokenUri: https://github.com/login/oauth/access_token
			userAuthorizationUri: https://github.com/login/oauth/authorize
			clientAuthenticationScheme: form

An application with this configuration will redirect to Github for authorization when you attempt to use the OAuth2RestTemplate. If you are already signed into Github you won’t even notice that it has authenticated. These specific credentials will only work if your application is running on port 8080 (register your own client app in Github or other provider for more flexibility).

To limit the scope that the client asks for when it obtains an access token you can set security.oauth2.client.scope (comma separated or an array in YAML). By default the scope is empty and it is up to Authorization Server to decide what the defaults should be, usually depending on the settings in the client registration that it holds.

Note

There is also a setting for security.oauth2.client.client-authentication-scheme which defaults to “header” (but you might need to set it to “form” if, like Github for instance, your OAuth2 provider doesn’t like header authentication). In fact, the security.oauth2.client.* properties are bound to an instance of AuthorizationCodeResourceDetails so all its properties can be specified.

Tip

In a non-web application you can still create an OAuth2RestOperations and it is still wired into the security.oauth2.client.* configuration. In this case it is a “client credentials token grant” you will be asking for if you use it (and there is no need to use @EnableOAuth2Client or @EnableOAuth2Sso). To prevent that infrastructure to be defined, just remove the security.oauth2.client.client-id from your configuration (or make it the empty string).

Single Sign On

An OAuth2 Client can be used to fetch user details from the provider (if such features are available) and then convert them into an Authentication token for Spring Security. The Resource Server above support this via the user-info-uri property This is the basis for a Single Sign On (SSO) protocol based on OAuth2, and Spring Boot makes it easy to participate by providing an annotation @EnableOAuth2Sso. The Github client above can protect all its resources and authenticate using the Github /user/ endpoint, by adding that annotation and declaring where to find the endpoint (in addition to the security.oauth2.client.* configuration already listed above):

application.yml

security:
	oauth2:
...
	resource:
		userInfoUri: https://api.github.com/user
		preferTokenInfo: false

Since all paths are secure by default, there is no “home” page that you can show to unauthenticated users and invite them to login (by visiting the /login path, or the path specified by security.oauth2.sso.login-path).

To customize the access rules or paths to protect, so you can add a “home” page for instance, @EnableOAuth2Sso can be added to a WebSecurityConfigurerAdapter and the annotation will cause it to be decorated and enhanced with the necessary pieces to get the /login path working. For example, here we simply allow unauthenticated access to the home page at "/" and keep the default for everything else:

link:{code-examples}/web/security/UnauthenticatedAccessExample.java[role=include]

Actuator Security

If the Actuator is also in use, you will find:

• The management endpoints are secure even if the application endpoints are insecure.

• Security events are transformed into AuditEvent instances and published to the AuditEventRepository.

• The default user will have the ACTUATOR role as well as the USER role.

The Actuator security features can be modified using external properties (management.security.*). To override the application access rules add a @Bean of type WebSecurityConfigurerAdapter and use @Order(SecurityProperties.ACCESS_OVERRIDE_ORDER) if you don’t want to override the actuator access rules, or @Order(ManagementServerProperties.ACCESS_OVERRIDE_ORDER) if you do want to override the actuator access rules.

Working with SQL databases

The Spring Framework provides extensive support for working with SQL databases. From direct JDBC access using JdbcTemplate to complete ‘object relational mapping’ technologies such as Hibernate. Spring Data provides an additional level of functionality, creating Repository implementations directly from interfaces and using conventions to generate queries from your method names.

Configure a DataSource

Java’s javax.sql.DataSource interface provides a standard method of working with database connections. Traditionally a DataSource uses a URL along with some credentials to establish a database connection.

Tip	Check also the ‘How-to’ section for more advanced examples, typically to take full control over the configuration of the DataSource.

Embedded Database Support

It’s often convenient to develop applications using an in-memory embedded database. Obviously, in-memory databases do not provide persistent storage; you will need to populate your database when your application starts and be prepared to throw away data when your application ends.

Tip	The ‘How-to’ section includes a section on how to initialize a database

Spring Boot can auto-configure embedded H2, HSQL and Derby databases. You don’t need to provide any connection URLs, simply include a build dependency to the embedded database that you want to use.

Note

If you are using this feature in your tests, you may notice that the same database is reused by your whole test suite regardless of the number of application contexts that you use. If you want to make sure that each context has a separate embedded database, you should set spring.datasource.generate-unique-name to true.

For example, typical POM dependencies would be:

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
	<groupId>org.hsqldb</groupId>
	<artifactId>hsqldb</artifactId>
	<scope>runtime</scope>
</dependency>

Note	You need a dependency on spring-jdbc for an embedded database to be auto-configured. In this example it’s pulled in transitively via spring-boot-starter-data-jpa.

Tip

If, for whatever reason, you do configure the connection URL for an embedded database, care should be taken to ensure that the database’s automatic shutdown is disabled. If you’re using H2 you should use DB_CLOSE_ON_EXIT=FALSE to do so. If you’re using HSQLDB, you should ensure that shutdown=true is not used. Disabling the database’s automatic shutdown allows Spring Boot to control when the database is closed, thereby ensuring that it happens once access to the database is no longer needed.

Connection to a production database

Production database connections can also be auto-configured using a pooling DataSource. Here’s the algorithm for choosing a specific implementation:

• We prefer HikariCP for its performance and concurrency, so if that is available we always choose it.

• Otherwise, if the Tomcat pooling DataSource is available we will use it.

• If neither HikariCP nor the Tomcat pooling datasource are available and if Commons DBCP2 is available we will use it.

If you use the spring-boot-starter-jdbc or spring-boot-starter-data-jpa ‘starters’ you will automatically get a dependency to tomcat-jdbc.

Note	You can bypass that algorithm completely and specify the connection pool to use via the spring.datasource.type property. This is especially important if you are running your application in a Tomcat container as tomcat-jdbc is provided by default.

Tip	Additional connection pools can always be configured manually. If you define your own DataSource bean, auto-configuration will not occur.

DataSource configuration is controlled by external configuration properties in spring.datasource.*. For example, you might declare the following section in application.properties:

spring.datasource.url=jdbc:mysql://localhost/test
spring.datasource.username=dbuser
spring.datasource.password=dbpass
spring.datasource.driver-class-name=com.mysql.jdbc.Driver

Note	You should at least specify the url using the spring.datasource.url property or Spring Boot will attempt to auto-configure an embedded database.

Tip	You often won’t need to specify the driver-class-name since Spring boot can deduce it for most databases from the url.

Note	For a pooling DataSource to be created we need to be able to verify that a valid Driver class is available, so we check for that before doing anything. I.e. if you set spring.datasource.driver-class-name=com.mysql.jdbc.Driver then that class has to be loadable.

See {sc-spring-boot-autoconfigure}/jdbc/DataSourceProperties.{sc-ext}[DataSourceProperties] for more of the supported options. These are the standard options that work regardless of the actual implementation. It is also possible to fine-tune implementation-specific settings using their respective prefix (spring.datasource.hikari.*, spring.datasource.tomcat.*, and spring.datasource.dbcp2.*). Refer to the documentation of the connection pool implementation you are using for more details.

For instance, if you are using the Tomcat connection pool you could customize many additional settings:

# Number of ms to wait before throwing an exception if no connection is available.
spring.datasource.tomcat.max-wait=10000

# Maximum number of active connections that can be allocated from this pool at the same time.
spring.datasource.tomcat.max-active=50

# Validate the connection before borrowing it from the pool.
spring.datasource.tomcat.test-on-borrow=true

Connection to a JNDI DataSource

If you are deploying your Spring Boot application to an Application Server you might want to configure and manage your DataSource using your Application Servers built-in features and access it using JNDI.

The spring.datasource.jndi-name property can be used as an alternative to the spring.datasource.url, spring.datasource.username and spring.datasource.password properties to access the DataSource from a specific JNDI location. For example, the following section in application.properties shows how you can access a JBoss AS defined DataSource:

spring.datasource.jndi-name=java:jboss/datasources/customers

Using JdbcTemplate

Spring’s JdbcTemplate and NamedParameterJdbcTemplate classes are auto-configured and you can @Autowire them directly into your own beans:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

	private final JdbcTemplate jdbcTemplate;

	@Autowired
	public MyBean(JdbcTemplate jdbcTemplate) {
		this.jdbcTemplate = jdbcTemplate;
	}

	// ...

}

JPA and ‘Spring Data’

The Java Persistence API is a standard technology that allows you to ‘map’ objects to relational databases. The spring-boot-starter-data-jpa POM provides a quick way to get started. It provides the following key dependencies:

• Hibernate — One of the most popular JPA implementations.

• Spring Data JPA — Makes it easy to implement JPA-based repositories.

• Spring ORMs — Core ORM support from the Spring Framework.

Tip	We won’t go into too many details of JPA or Spring Data here. You can follow the ‘Accessing Data with JPA’ guide from http://spring.io and read the Spring Data JPA and Hibernate reference documentation.

Entity Classes

Traditionally, JPA ‘Entity’ classes are specified in a persistence.xml file. With Spring Boot this file is not necessary and instead ‘Entity Scanning’ is used. By default all packages below your main configuration class (the one annotated with @EnableAutoConfiguration or @SpringBootApplication) will be searched.

Any classes annotated with @Entity, @Embeddable or @MappedSuperclass will be considered. A typical entity class would look something like this:

package com.example.myapp.domain;

import java.io.Serializable;
import javax.persistence.*;

@Entity
public class City implements Serializable {

	@Id
	@GeneratedValue
	private Long id;

	@Column(nullable = false)
	private String name;

	@Column(nullable = false)
	private String state;

	// ... additional members, often include @OneToMany mappings

	protected City() {
		// no-args constructor required by JPA spec
		// this one is protected since it shouldn't be used directly
	}

	public City(String name, String state) {
		this.name = name;
		this.country = country;
	}

	public String getName() {
		return this.name;
	}

	public String getState() {
		return this.state;
	}

	// ... etc

}

Tip	You can customize entity scanning locations using the @EntityScan annotation. See the howto.adoc how-to.

Spring Data JPA Repositories

Spring Data JPA repositories are interfaces that you can define to access data. JPA queries are created automatically from your method names. For example, a CityRepository interface might declare a findAllByState(String state) method to find all cities in a given state.

For more complex queries you can annotate your method using Spring Data’s {spring-data-javadoc}/repository/Query.html[Query] annotation.

Spring Data repositories usually extend from the {spring-data-commons-javadoc}/repository/Repository.html[Repository] or {spring-data-commons-javadoc}/repository/CrudRepository.html[CrudRepository] interfaces. If you are using auto-configuration, repositories will be searched from the package containing your main configuration class (the one annotated with @EnableAutoConfiguration or @SpringBootApplication) down.

Here is a typical Spring Data repository:

package com.example.myapp.domain;

import org.springframework.data.domain.*;
import org.springframework.data.repository.*;

public interface CityRepository extends Repository<City, Long> {

	Page<City> findAll(Pageable pageable);

	City findByNameAndCountryAllIgnoringCase(String name, String country);

}

Tip	We have barely scratched the surface of Spring Data JPA. For complete details check their reference documentation.

Creating and dropping JPA databases

By default, JPA databases will be automatically created only if you use an embedded database (H2, HSQL or Derby). You can explicitly configure JPA settings using spring.jpa.* properties. For example, to create and drop tables you can add the following to your application.properties.

spring.jpa.hibernate.ddl-auto=create-drop

Note	Hibernate’s own internal property name for this (if you happen to remember it better) is hibernate.hbm2ddl.auto. You can set it, along with other Hibernate native properties, using spring.jpa.properties.* (the prefix is stripped before adding them to the entity manager). Example:

spring.jpa.properties.hibernate.globally_quoted_identifiers=true

passes hibernate.globally_quoted_identifiers to the Hibernate entity manager.

By default the DDL execution (or validation) is deferred until the ApplicationContext has started. There is also a spring.jpa.generate-ddl flag, but it is not used if Hibernate autoconfig is active because the ddl-auto settings are more fine-grained.

Open EntityManager in View

If you are running a web application, Spring Boot will by default register {spring-javadoc}/orm/jpa/support/OpenEntityManagerInViewInterceptor.html[OpenEntityManagerInViewInterceptor] to apply the "Open EntityManager in View" pattern, i.e. to allow for lazy loading in web views. If you don’t want this behavior you should set spring.jpa.open-in-view to false in your application.properties.

Using H2’s web console

The H2 database provides a browser-based console that Spring Boot can auto-configure for you. The console will be auto-configured when the following conditions are met:

• You are developing a web application

• com.h2database:h2 is on the classpath

• You are using Spring Boot’s developer tools

Tip

If you are not using Spring Boot’s developer tools, but would still like to make use of H2’s console, then you can do so by configuring the spring.h2.console.enabled property with a value of true. The H2 console is only intended for use during development so care should be taken to ensure that spring.h2.console.enabled is not set to true in production.

Changing the H2 console’s path

By default the console will be available at /h2-console. You can customize the console’s path using the spring.h2.console.path property.

Securing the H2 console

When Spring Security is on the classpath and basic auth is enabled, the H2 console will be automatically secured using basic auth. The following properties can be used to customize the security configuration:

• security.user.role

• security.basic.authorize-mode

• security.basic.enabled

Using jOOQ

Java Object Oriented Querying (jOOQ) is a popular product from Data Geekery which generates Java code from your database, and lets you build type safe SQL queries through its fluent API. Both the commercial and open source editions can be used with Spring Boot.

Code Generation

In order to use jOOQ type-safe queries, you need to generate Java classes from your database schema. You can follow the instructions in the jOOQ user manual. If you are using the jooq-codegen-maven plugin (and you also use the spring-boot-starter-parent “parent POM”) you can safely omit the plugin’s <version> tag. You can also use Spring Boot defined version variables (e.g. h2.version) to declare the plugin’s database dependency. Here’s an example:

<plugin>
	<groupId>org.jooq</groupId>
	<artifactId>jooq-codegen-maven</artifactId>
	<executions>
		...
	</executions>
	<dependencies>
		<dependency>
			<groupId>com.h2database</groupId>
			<artifactId>h2</artifactId>
			<version>${h2.version}</version>
		</dependency>
	</dependencies>
	<configuration>
		<jdbc>
			<driver>org.h2.Driver</driver>
			<url>jdbc:h2:~/yourdatabase</url>
		</jdbc>
		<generator>
			...
		</generator>
	</configuration>
</plugin>

Using DSLContext

The fluent API offered by jOOQ is initiated via the org.jooq.DSLContext interface. Spring Boot will auto-configure a DSLContext as a Spring Bean and connect it to your application DataSource. To use the DSLContext you can just @Autowire it:

@Component
public class JooqExample implements CommandLineRunner {

	private final DSLContext create;

	@Autowired
	public JooqExample(DSLContext dslContext) {
		this.create = dslContext;
	}

}

Tip	The jOOQ manual tends to use a variable named create to hold the DSLContext, we’ve done the same for this example.

You can then use the DSLContext to construct your queries:

public List<GregorianCalendar> authorsBornAfter1980() {
	return this.create.selectFrom(AUTHOR)
		.where(AUTHOR.DATE_OF_BIRTH.greaterThan(new GregorianCalendar(1980, 0, 1)))
		.fetch(AUTHOR.DATE_OF_BIRTH);
}

jOOQ SQL dialect

Spring Boot determines the SQL dialect to use for your datasource unless the spring.jooq.sql-dialect property has been configured. If the dialect couldn’t be detected, DEFAULT is used.

Note	Spring Boot can only auto-configure dialects supported by the open source version of jOOQ.

Customizing jOOQ

More advanced customizations can be achieved by defining your own @Bean definitions which will be used when the jOOQ Configuration is created. You can define beans for the following jOOQ Types:

• ConnectionProvider

• TransactionProvider

• RecordMapperProvider

• RecordListenerProvider

• ExecuteListenerProvider

• VisitListenerProvider

You can also create your own org.jooq.Configuration @Bean if you want to take complete control of the jOOQ configuration.

Working with NoSQL technologies

Spring Data provides additional projects that help you access a variety of NoSQL technologies including MongoDB, Neo4J, Elasticsearch, Solr, Redis, Gemfire, Cassandra, Couchbase and LDAP. Spring Boot provides auto-configuration for Redis, MongoDB, Neo4j, Elasticsearch, Solr Cassandra, Couchbase and LDAP; you can make use of the other projects, but you will need to configure them yourself. Refer to the appropriate reference documentation at projects.spring.io/spring-data.

Redis

Redis is a cache, message broker and richly-featured key-value store. Spring Boot offers basic auto-configuration for the Jedis and Lettuce client library and abstractions on top of it provided by Spring Data Redis.

There is a spring-boot-starter-data-redis ‘Starter’ for collecting the dependencies in a convenient way that uses Jedis by default. If you are building a reactive application, the spring-boot-starter-data-redis-reactive ‘Starter’ will get you going.

Connecting to Redis

You can inject an auto-configured RedisConnectionFactory, StringRedisTemplate or vanilla RedisTemplate instance as you would any other Spring Bean. By default the instance will attempt to connect to a Redis server using localhost:6379:

@Component
public class MyBean {

	private StringRedisTemplate template;

	@Autowired
	public MyBean(StringRedisTemplate template) {
		this.template = template;
	}

	// ...

}

If you add a @Bean of your own of any of the auto-configured types it will replace the default (except in the case of RedisTemplate the exclusion is based on the bean name ‘redisTemplate’ not its type). If commons-pool2 is on the classpath you will get a pooled connection factory by default.

MongoDB

MongoDB is an open-source NoSQL document database that uses a JSON-like schema instead of traditional table-based relational data. Spring Boot offers several conveniences for working with MongoDB, including the spring-boot-starter-data-mongodb and spring-boot-starter-data-mongodb-reactive ‘Starters’.

Connecting to a MongoDB database

You can inject an auto-configured org.springframework.data.mongodb.MongoDbFactory to access Mongo databases. By default the instance will attempt to connect to a MongoDB server using the URL mongodb://localhost/test:

import org.springframework.data.mongodb.MongoDbFactory;
import com.mongodb.DB;

@Component
public class MyBean {

	private final MongoDbFactory mongo;

	@Autowired
	public MyBean(MongoDbFactory mongo) {
		this.mongo = mongo;
	}

	// ...

	public void example() {
		DB db = mongo.getDb();
		// ...
	}

}

You can set spring.data.mongodb.uri property to change the URL and configure additional settings such as the replica set:

spring.data.mongodb.uri=mongodb://user:secret@mongo1.example.com:12345,mongo2.example.com:23456/test

Alternatively, as long as you’re using Mongo 2.x, specify a host/port. For example, you might declare the following in your application.properties:

spring.data.mongodb.host=mongoserver
spring.data.mongodb.port=27017

Note	spring.data.mongodb.host and spring.data.mongodb.port are not supported if you’re using the Mongo 3.0 Java driver. In such cases, spring.data.mongodb.uri should be used to provide all of the configuration.

Tip	If spring.data.mongodb.port is not specified the default of 27017 is used. You could simply delete this line from the sample above.

Tip	If you aren’t using Spring Data Mongo you can inject com.mongodb.Mongo beans instead of using MongoDbFactory.

You can also declare your own MongoDbFactory or Mongo bean if you want to take complete control of establishing the MongoDB connection.

MongoTemplate

Spring Data Mongo provides a {spring-data-mongo-javadoc}/core/MongoTemplate.html[MongoTemplate] class that is very similar in its design to Spring’s JdbcTemplate. As with JdbcTemplate Spring Boot auto-configures a bean for you to simply inject:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

	private final MongoTemplate mongoTemplate;

	@Autowired
	public MyBean(MongoTemplate mongoTemplate) {
		this.mongoTemplate = mongoTemplate;
	}

	// ...

}

See the MongoOperations Javadoc for complete details.

Spring Data MongoDB repositories

Spring Data includes repository support for MongoDB. As with the JPA repositories discussed earlier, the basic principle is that queries are constructed for you automatically based on method names.

In fact, both Spring Data JPA and Spring Data MongoDB share the same common infrastructure; so you could take the JPA example from earlier and, assuming that City is now a Mongo data class rather than a JPA @Entity, it will work in the same way.

package com.example.myapp.domain;

import org.springframework.data.domain.*;
import org.springframework.data.repository.*;

public interface CityRepository extends Repository<City, Long> {

	Page<City> findAll(Pageable pageable);

	City findByNameAndCountryAllIgnoringCase(String name, String country);

}

Tip	For complete details of Spring Data MongoDB, including its rich object mapping technologies, refer to their reference documentation.

Embedded Mongo

Spring Boot offers auto-configuration for Embedded Mongo. To use it in your Spring Boot application add a dependency on de.flapdoodle.embed:de.flapdoodle.embed.mongo.

The port that Mongo will listen on can be configured using the spring.data.mongodb.port property. To use a randomly allocated free port use a value of zero. The MongoClient created by MongoAutoConfiguration will be automatically configured to use the randomly allocated port.

Note	If you do not configure a custom port, the embedded support will use a random port by default (rather than 27017).

If you have SLF4J on the classpath, output produced by Mongo will be automatically routed to a logger named org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongo.

You can declare your own IMongodConfig and IRuntimeConfig beans to take control of the Mongo instance’s configuration and logging routing.

Neo4j

Neo4j is an open-source NoSQL graph database that uses a rich data model of nodes related by first class relationships which is better suited for connected big data than traditional rdbms approaches. Spring Boot offers several conveniences for working with Neo4j, including the spring-boot-starter-data-neo4j ‘Starter’.

Connecting to a Neo4j database

You can inject an auto-configured Neo4jSession, Session or Neo4jOperations instance as you would any other Spring Bean. By default the instance will attempt to connect to a Neo4j server using localhost:7474:

@Component
public class MyBean {

	private final Neo4jTemplate neo4jTemplate;

	@Autowired
	public MyBean(Neo4jTemplate neo4jTemplate) {
		this.neo4jTemplate = neo4jTemplate;
	}

	// ...

}

You can take full control of the configuration by adding a org.neo4j.ogm.config.Configuration @Bean of your own. Also, adding a @Bean of type Neo4jOperations disables the auto-configuration.

You can configure the user and credentials to use via the spring.data.neo4j.* properties:

spring.data.neo4j.uri=http://my-server:7474
spring.data.neo4j.username=neo4j
spring.data.neo4j.password=secret

Using the embedded mode

If you add org.neo4j:neo4j-ogm-embedded-driver to the dependencies of your application, Spring Boot will automatically configure an in-process embedded instance of Neo4j that will not persist any data when your application shuts down. You can explicitly disable that mode using spring.data.neo4j.embedded.enabled=false. You can also enable persistence for the embedded mode:

	spring.data.neo4j.uri=file://var/tmp/graph.db

Note	The Neo4j OGM embedded driver does not provide the Neo4j kernel. Users are expected to provide this dependency manually, see the documentation for more details.

Neo4jSession

By default, if you are running a web application, the session is bound to the thread for the entire processing of the request (i.e. the "Open Session in View" pattern). If you don’t want this behavior add the following to your application.properties:

	spring.data.neo4j.open-in-view=false

Spring Data Neo4j repositories

Spring Data includes repository support for Neo4j.

In fact, both Spring Data JPA and Spring Data Neo4j share the same common infrastructure; so you could take the JPA example from earlier and, assuming that City is now a Neo4j OGM @NodeEntity rather than a JPA @Entity, it will work in the same way.

Tip	You can customize entity scanning locations using the @EntityScan annotation.

To enable repository support (and optionally support for @Transactional), add the following two annotations to your Spring configuration:

@EnableNeo4jRepositories(basePackages = "com.example.myapp.repository")
@EnableTransactionManagement

Repository example

package com.example.myapp.domain;

import org.springframework.data.domain.*;
import org.springframework.data.repository.*;

public interface CityRepository extends GraphRepository<City> {

	Page<City> findAll(Pageable pageable);

	City findByNameAndCountry(String name, String country);

}

Tip	For complete details of Spring Data Neo4j, including its rich object mapping technologies, refer to their reference documentation.

Gemfire

Spring Data Gemfire provides convenient Spring-friendly tools for accessing the Pivotal Gemfire data management platform. There is a spring-boot-starter-data-gemfire ‘Starter’ for collecting the dependencies in a convenient way. There is currently no auto-configuration support for Gemfire, but you can enable Spring Data Repositories with a single annotation (@EnableGemfireRepositories).

Solr

Apache Solr is a search engine. Spring Boot offers basic auto-configuration for the Solr 5 client library and abstractions on top of it provided by Spring Data Solr. There is a spring-boot-starter-data-solr ‘Starter’ for collecting the dependencies in a convenient way.

Connecting to Solr

You can inject an auto-configured SolrClient instance as you would any other Spring bean. By default the instance will attempt to connect to a server using http://localhost:8983/solr:

@Component
public class MyBean {

	private SolrClient solr;

	@Autowired
	public MyBean(SolrClient solr) {
		this.solr = solr;
	}

	// ...

}

If you add a @Bean of your own of type SolrClient it will replace the default.

Spring Data Solr repositories

Spring Data includes repository support for Apache Solr. As with the JPA repositories discussed earlier, the basic principle is that queries are constructed for you automatically based on method names.

In fact, both Spring Data JPA and Spring Data Solr share the same common infrastructure; so you could take the JPA example from earlier and, assuming that City is now a @SolrDocument class rather than a JPA @Entity, it will work in the same way.

Tip	For complete details of Spring Data Solr, refer to their reference documentation.

Elasticsearch

Elasticsearch is an open source, distributed, real-time search and analytics engine. Spring Boot offers basic auto-configuration for the Elasticsearch and abstractions on top of it provided by Spring Data Elasticsearch. There is a spring-boot-starter-data-elasticsearch ‘Starter’ for collecting the dependencies in a convenient way. Spring Boot also supports Jest.

Connecting to Elasticsearch using Jest

If you have Jest on the classpath, you can inject an auto-configured JestClient targeting http://localhost:9200 by default. You can further tune how the client is configured:

spring.elasticsearch.jest.uris=http://search.example.com:9200
spring.elasticsearch.jest.read-timeout=10000
spring.elasticsearch.jest.username=user
spring.elasticsearch.jest.password=secret

You can also register an arbitrary number of beans implementing HttpClientConfigBuilderCustomizer for more advanced customizations. The example below tunes additional HTTP settings:

link:{code-examples}/elasticsearch/jest/JestClientCustomizationExample.java[role=include]

To take full control over the registration, define a JestClient bean.

Connecting to Elasticsearch using Spring Data

You can inject an auto-configured ElasticsearchTemplate or Elasticsearch Client instance as you would any other Spring Bean. By default the instance will embed a local in-memory server (a Node in Elasticsearch terms) and use the current working directory as the home directory for the server. In this setup, the first thing to do is to tell Elasticsearch where to store its files:

spring.data.elasticsearch.properties.path.home=/foo/bar

Alternatively, you can switch to a remote server (i.e. a TransportClient) by setting spring.data.elasticsearch.cluster-nodes to a comma-separated ‘host:port’ list.

spring.data.elasticsearch.cluster-nodes=localhost:9300

@Component
public class MyBean {

	private ElasticsearchTemplate template;

	@Autowired
	public MyBean(ElasticsearchTemplate template) {
		this.template = template;
	}

	// ...

}

If you add a @Bean of your own of type ElasticsearchTemplate it will replace the default.

Spring Data Elasticsearch repositories

Spring Data includes repository support for Elasticsearch. As with the JPA repositories discussed earlier, the basic principle is that queries are constructed for you automatically based on method names.

In fact, both Spring Data JPA and Spring Data Elasticsearch share the same common infrastructure; so you could take the JPA example from earlier and, assuming that City is now an Elasticsearch @Document class rather than a JPA @Entity, it will work in the same way.

Tip	For complete details of Spring Data Elasticsearch, refer to their reference documentation.

Cassandra

Cassandra is an open source, distributed database management system designed to handle large amounts of data across many commodity servers. Spring Boot offers auto-configuration for Cassandra and abstractions on top of it provided by Spring Data Cassandra. There is a spring-boot-starter-data-cassandra ‘Starter’ for collecting the dependencies in a convenient way.

Connecting to Cassandra

You can inject an auto-configured CassandraTemplate or a Cassandra Session instance as you would with any other Spring Bean. The spring.data.cassandra.* properties can be used to customize the connection. Generally you will provide keyspace-name and contact-points properties:

spring.data.cassandra.keyspace-name=mykeyspace
spring.data.cassandra.contact-points=cassandrahost1,cassandrahost2

@Component
public class MyBean {

	private CassandraTemplate template;

	@Autowired
	public MyBean(CassandraTemplate template) {
		this.template = template;
	}

	// ...

}

If you add a @Bean of your own of type CassandraTemplate it will replace the default.

Spring Data Cassandra repositories

Spring Data includes basic repository support for Cassandra. Currently this is more limited than the JPA repositories discussed earlier, and will need to annotate finder methods with @Query.

Tip	For complete details of Spring Data Cassandra, refer to their reference documentation.

Couchbase

Couchbase is an open-source, distributed multi-model NoSQL document-oriented database that is optimized for interactive applications. Spring Boot offers auto-configuration for Couchbase and abstractions on top of it provided by Spring Data Couchbase. There is a spring-boot-starter-data-couchbase ‘Starter’ for collecting the dependencies in a convenient way.

Connecting to Couchbase

You can very easily get a Bucket and Cluster by adding the Couchbase SDK and some configuration. The spring.couchbase.* properties can be used to customize the connection. Generally you will provide the bootstrap hosts, bucket name and password:

spring.couchbase.bootstrap-hosts=my-host-1,192.168.1.123
spring.couchbase.bucket.name=my-bucket
spring.couchbase.bucket.password=secret

Tip	You need to provide at least the bootstrap host(s), in which case the bucket name is default and the password is the empty String. Alternatively, you can define your own org.springframework.data.couchbase.config.CouchbaseConfigurer @Bean to take control over the whole configuration.

It is also possible to customize some of the CouchbaseEnvironment settings. For instance the following configuration changes the timeout to use to open a new Bucket and enables SSL support:

spring.couchbase.env.timeouts.connect=3000
spring.couchbase.env.ssl.key-store=/location/of/keystore.jks
spring.couchbase.env.ssl.key-store-password=secret

Check the spring.couchbase.env.* properties for more details.

Spring Data Couchbase repositories

Spring Data includes repository support for Couchbase. For complete details of Spring Data Couchbase, refer to their reference documentation.

You can inject an auto-configured CouchbaseTemplate instance as you would with any other Spring Bean as long as a default CouchbaseConfigurer is available (that happens when you enable the couchbase support as explained above).

@Component
public class MyBean {

	private final CouchbaseTemplate template;

	@Autowired
	public MyBean(CouchbaseTemplate template) {
		this.template = template;
	}

	// ...

}

There are a few beans that you can define in your own configuration to override those provided by the auto-configuration:

• A CouchbaseTemplate @Bean with name couchbaseTemplate

• An IndexManager @Bean with name couchbaseIndexManager

• A CustomConversions @Bean with name couchbaseCustomConversions

To avoid hard-coding those names in your own config, you can reuse BeanNames provided by Spring Data Couchbase. For instance, you can customize the converters to use as follows:

@Configuration
public class SomeConfiguration {

	@Bean(BeanNames.COUCHBASE_CUSTOM_CONVERSIONS)
	public CustomConversions myCustomConversions() {
		return new CustomConversions(...);
	}

	// ...

}

Tip	If you want to fully bypass the auto-configuration for Spring Data Couchbase, provide your own org.springframework.data.couchbase.config.AbstractCouchbaseDataConfiguration implementation.

LDAP

LDAP (Lightweight Directory Access Protocol) is an open, vendor-neutral, industry standard application protocol for accessing and maintaining distributed directory information services over an IP network. Spring Boot offers auto-configuration for any compliant LDAP server as well as support for the embedded in-memory LDAP server from UnboundID.

LDAP abstractions are provided by Spring Data LDAP. There is a spring-boot-starter-data-ldap ‘Starter’ for collecting the dependencies in a convenient way.

Connecting to an LDAP server

To connect to an LDAP server make sure you declare a dependency on the spring-boot-starter-data-ldap ‘Starter’ or spring-ldap-core then declare the URLs of your server in your application.properties:

spring.ldap.urls=ldap://myserver:1235
spring.ldap.username=admin
spring.ldap.password=secret

If you need to customize connection settings you can use the spring.ldap.base and spring.ldap.base-environment properties.

Spring Data LDAP repositories

Spring Data includes repository support for LDAP. For complete details of Spring Data LDAP, refer to their reference documentation.

You can also inject an auto-configured LdapTemplate instance as you would with any other Spring Bean.

@Component
public class MyBean {

	private final LdapTemplate template;

	@Autowired
	public MyBean(LdapTemplate template) {
		this.template = template;
	}

	// ...

}

Embedded in-memory LDAP server

For testing purposes Spring Boot supports auto-configuration of an in-memory LDAP server from UnboundID. To configure the server add a dependency to com.unboundid:unboundid-ldapsdk and declare a base-dn property:

spring.ldap.embedded.base-dn=dc=spring,dc=io

By default the server will start on a random port and they trigger the regular LDAP support (there is no need to specify a spring.ldap.urls property).

If there is a schema.ldif file on your classpath it will be used to initialize the server. You can also use the spring.ldap.embedded.ldif property if you want to load the initialization script from a different resource.

By default, a standard schema will be used to validate LDIF files, you can turn off validation altogether using the spring.ldap.embedded.validation.enabled property. If you have custom attributes, you can use spring.ldap.embedded.validation.schema to define your custom attribute types or object classes.

Caching

The Spring Framework provides support for transparently adding caching to an application. At its core, the abstraction applies caching to methods, reducing thus the number of executions based on the information available in the cache. The caching logic is applied transparently, without any interference to the invoker. Spring Boot auto-configures the cache infrastructure as long as the caching support is enabled via the @EnableCaching annotation.

Note	Check the {spring-reference}/#cache[relevant section] of the Spring Framework reference for more details.

In a nutshell, adding caching to an operation of your service is as easy as adding the relevant annotation to its method:

   import org.springframework.cache.annotation.Cacheable
import org.springframework.stereotype.Component;

@Component
public class MathService {

	@Cacheable("piDecimals")
	public int computePiDecimal(int i) {
		// ...
	}

}

This example demonstrates the use of caching on a potentially costly operation. Before invoking computePiDecimal, the abstraction will look for an entry in the piDecimals cache matching the i argument. If an entry is found, the content in the cache is immediately returned to the caller and the method is not invoked. Otherwise, the method is invoked and the cache is updated before returning the value.

Note	You can also use the standard JSR-107 (JCache) annotations (e.g. @CacheResult) transparently. We strongly advise you however to not mix and match them.

If you do not add any specific cache library, Spring Boot will auto-configure a Simple provider that uses concurrent maps in memory. When a cache is required (i.e. piDecimals in the example above), this provider will create it on-the-fly for you. The simple provider is not really recommended for production usage, but it’s great for getting started and making sure that you understand the features. When you have made up your mind about the cache provider to use, please make sure to read its documentation to figure out how to configure the caches that your application uses. Practically all providers require you to explicitly configure every cache that you use in the application. Some offer a way to customize the default caches defined by the spring.cache.cache-names property.

Tip	It is also possible to {spring-reference}/#cache-annotations-put[update] or {spring-reference}/#cache-annotations-evict[evict] data from the cache transparently.

Note	If you are using the cache infrastructure with beans that are not interface-based, make sure to enable the proxyTargetClass attribute of @EnableCaching.

Supported cache providers

The cache abstraction does not provide an actual store and relies on abstraction materialized by the org.springframework.cache.Cache and org.springframework.cache.CacheManager interfaces.

If you haven’t defined a bean of type CacheManager or a CacheResolver named cacheResolver (see CachingConfigurer), Spring Boot tries to detect the following providers (in this order):

• Generic

• JCache (JSR-107) (EhCache 3, Hazelcast, Infinispan, etc)

• EhCache 2.x

• Hazelcast

• Infinispan

• Couchbase

• Redis

• Caffeine

• Simple

Tip	It is also possible to force the cache provider to use via the spring.cache.type property. Use this property if you need to disable caching altogether in certain environment (e.g. tests).

Tip	Use the spring-boot-starter-cache ‘Starter’ to quickly add basic caching dependencies. The starter brings in spring-context-support: if you are adding dependencies manually, you must include spring-context-support in order to use the JCache, EhCache 2.x or Guava support.

If the CacheManager is auto-configured by Spring Boot, you can further tune its configuration before it is fully initialized by exposing a bean implementing the CacheManagerCustomizer interface. The following sets a flag to say that null values should be passed down to the underlying map.

@Bean
public CacheManagerCustomizer<ConcurrentMapCacheManager> cacheManagerCustomizer() {
	return new CacheManagerCustomizer<ConcurrentMapCacheManager>() {
		@Override
		public void customize(ConcurrentMapCacheManager cacheManager) {
			cacheManager.setAllowNullValues(false);
		}
	};
}

Note

In the example above, an auto-configured ConcurrentMapCacheManager is expected. If that is not the case (either you provided your own config or a different cache provider was auto-configured), the customizer won’t be invoked at all. You can have as many customizers as you want and you can also order them as usual using @Order or Ordered.

Generic

Generic caching is used if the context defines at least one org.springframework.cache.Cache bean. A CacheManager wrapping all beans of that type is created.

JCache (JSR-107)

JCache is bootstrapped via the presence of a javax.cache.spi.CachingProvider on the classpath (i.e. a JSR-107 compliant caching library) and the JCacheCacheManager provided by the spring-boot-starter-cache ‘Starter’. There are various compliant libraries out there and Spring Boot provides dependency management for Ehcache 3, Hazelcast and Infinispan. Any other compliant library can be added as well.

It might happen that more than one provider is present, in which case the provider must be explicitly specified. Even if the JSR-107 standard does not enforce a standardized way to define the location of the configuration file, Spring Boot does its best to accommodate with implementation details.

   # Only necessary if more than one provider is present
spring.cache.jcache.provider=com.acme.MyCachingProvider
spring.cache.jcache.config=classpath:acme.xml

Note	Since a cache library may offer both a native implementation and JSR-107 support Spring Boot will prefer the JSR-107 support so that the same features are available if you switch to a different JSR-107 implementation.

Tip	Spring Boot has a general support for Hazelcast. If a single HazelcastInstance is available, it is automatically reused for the CacheManager as well unless the spring.cache.jcache.config property is specified.

There are several ways to customize the underlying javax.cache.cacheManager:

• Caches can be created on startup via the spring.cache.cache-names property. If a custom javax.cache.configuration.Configuration bean is defined, it is used to customize them.

• org.springframework.boot.autoconfigure.cache.JCacheManagerCustomizer beans are invoked with the reference of the CacheManager for full customization.

Tip	If a standard javax.cache.CacheManager bean is defined, it is wrapped automatically in a org.springframework.cache.CacheManager implementation that the abstraction expects. No further customization is applied on it.

EhCache 2.x

EhCache 2.x is used if a file named ehcache.xml can be found at the root of the classpath. If EhCache 2.x, the EhCacheCacheManager provided by the spring-boot-starter-cache ‘Starter’ and such file is present it is used to bootstrap the cache manager. An alternate configuration file can be provided as well using:

spring.cache.ehcache.config=classpath:config/another-config.xml

Hazelcast

Spring Boot has a general support for Hazelcast. If a HazelcastInstance has been auto-configured, it is automatically wrapped in a CacheManager.

Infinispan

Infinispan has no default configuration file location so it must be specified explicitly (or the default bootstrap is used).

spring.cache.infinispan.config=infinispan.xml

Caches can be created on startup via the spring.cache.cache-names property. If a custom ConfigurationBuilder bean is defined, it is used to customize them.

Note	The support of Infinispan in Spring Boot is restricted to the embedded mode and is quite basic. If you want more options you should use the official Infinispan Spring Boot starter instead, check the documentation for more details.

Couchbase

If the Couchbase java client and the couchbase-spring-cache implementation are available and Couchbase is configured, a CouchbaseCacheManager will be auto-configured. It is also possible to create additional caches on startup using the spring.cache.cache-names property. These will operate on the Bucket that was auto-configured. You can also create additional caches on another Bucket using the customizer: assume you need two caches on the "main" Bucket (foo and bar) and one biz cache with a custom time to live of 2sec on the another Bucket. First, you can create the two first caches simply via configuration:

spring.cache.cache-names=foo,bar

Then define this extra @Configuration to configure the extra Bucket and the biz cache:

@Configuration
public class CouchbaseCacheConfiguration {

	private final Cluster cluster;

	public CouchbaseCacheConfiguration(Cluster cluster) {
		this.cluster = cluster;
	}

	@Bean
	public Bucket anotherBucket() {
		return this.cluster.openBucket("another", "secret");
	}

	@Bean
	public CacheManagerCustomizer<CouchbaseCacheManager> cacheManagerCustomizer() {
		return c -> {
			c.prepareCache("biz", CacheBuilder.newInstance(anotherBucket())
					.withExpiration(2));
		};
	}

}

This sample configuration reuses the Cluster that was created via auto-configuration.

Redis

If Redis is available and configured, the RedisCacheManager is auto-configured. It is also possible to create additional caches on startup using the spring.cache.cache-names property.

Note	By default, a key prefix is added to prevent that if two separate caches use the same key, Redis would have overlapping keys and be likely to return invalid values. We strongly recommend to keep this setting enabled if you create your own RedisCacheManager.

Caffeine

Caffeine is a Java 8 rewrite of Guava’s cache that supersede the Guava support. If Caffeine is present, a CaffeineCacheManager (provided by the spring-boot-starter-cache ‘Starter’) is auto-configured. Caches can be created on startup using the spring.cache.cache-names property and customized by one of the following (in this order):

1. A cache spec defined by spring.cache.caffeine.spec

2. A com.github.benmanes.caffeine.cache.CaffeineSpec bean is defined

3. A com.github.benmanes.caffeine.cache.Caffeine bean is defined

For instance, the following configuration creates a foo and bar caches with a maximum size of 500 and a time to live of 10 minutes

   spring.cache.cache-names=foo,bar
spring.cache.caffeine.spec=maximumSize=500,expireAfterAccess=600s

Besides, if a com.github.benmanes.caffeine.cache.CacheLoader bean is defined, it is automatically associated to the CaffeineCacheManager. Since the CacheLoader is going to be associated to all caches managed by the cache manager, it must be defined as CacheLoader<Object, Object>. Any other generic type will be ignored by the auto-configuration.

Simple

If none of the other providers can be found, a simple implementation using a ConcurrentHashMap as cache store is configured. This is the default if no caching library is present in your application. Caches are created on-the-fly by default but you can restrict the list of available caches using the cache-names property. For instance, if you want only foo and bar caches:

spring.cache.cache-names=foo,bar

If you do this and your application uses a cache not listed then it will fail at runtime when the cache is needed, but not on startup. This is similar to the way the "real" cache providers behave if you use an undeclared cache.

None

When @EnableCaching is present in your configuration, a suitable cache configuration is expected as well. If you need to disable caching altogether in certain environments, force the cache type to none to use a no-op implementation:

spring.cache.type=none

Messaging

The Spring Framework provides extensive support for integrating with messaging systems: from simplified use of the JMS API using JmsTemplate to a complete infrastructure to receive messages asynchronously. Spring AMQP provides a similar feature set for the ‘Advanced Message Queuing Protocol’ and Spring Boot also provides auto-configuration options for RabbitTemplate and RabbitMQ. There is also support for STOMP messaging natively in Spring WebSocket and Spring Boot has support for that through starters and a small amount of auto-configuration. Spring Boot also has support for Apache Kafka.

JMS

The javax.jms.ConnectionFactory interface provides a standard method of creating a javax.jms.Connection for interacting with a JMS broker. Although Spring needs a ConnectionFactory to work with JMS, you generally won’t need to use it directly yourself and you can instead rely on higher level messaging abstractions (see the {spring-reference}/#jms[relevant section] of the Spring Framework reference documentation for details). Spring Boot also auto-configures the necessary infrastructure to send and receive messages.

ActiveMQ support

Spring Boot can also configure a ConnectionFactory when it detects that ActiveMQ is available on the classpath. If the broker is present, an embedded broker is started and configured automatically (as long as no broker URL is specified through configuration).

Note	If you are using spring-boot-starter-activemq the necessary dependencies to connect or embed an ActiveMQ instance are provided, as well as the Spring infrastructure to integrate with JMS.

ActiveMQ configuration is controlled by external configuration properties in spring.activemq.*. For example, you might declare the following section in application.properties:

spring.activemq.broker-url=tcp://192.168.1.210:9876
spring.activemq.user=admin
spring.activemq.password=secret

You can also pool JMS resources by adding a dependency to org.apache.activemq:activemq-pool and configure the PooledConnectionFactory accordingly:

spring.activemq.pool.enabled=true
spring.activemq.pool.max-connections=50

See {sc-spring-boot-autoconfigure}/jms/activemq/ActiveMQProperties.{sc-ext}[ActiveMQProperties] for more of the supported options.

By default, ActiveMQ creates a destination if it does not exist yet, so destinations are resolved against their provided names.

Artemis support

Spring Boot can auto-configure a ConnectionFactory when it detects that Artemis is available on the classpath. If the broker is present, an embedded broker is started and configured automatically (unless the mode property has been explicitly set). The supported modes are: embedded (to make explicit that an embedded broker is required and should lead to an error if the broker is not available in the classpath), and native to connect to a broker using the netty transport protocol. When the latter is configured, Spring Boot configures a ConnectionFactory connecting to a broker running on the local machine with the default settings.

Note	If you are using spring-boot-starter-artemis the necessary dependencies to connect to an existing Artemis instance are provided, as well as the Spring infrastructure to integrate with JMS. Adding org.apache.activemq:artemis-jms-server to your application allows you to use the embedded mode.

Artemis configuration is controlled by external configuration properties in spring.artemis.*. For example, you might declare the following section in application.properties:

spring.artemis.mode=native
spring.artemis.host=192.168.1.210
spring.artemis.port=9876
spring.artemis.user=admin
spring.artemis.password=secret

When embedding the broker, you can choose if you want to enable persistence, and the list of destinations that should be made available. These can be specified as a comma-separated list to create them with the default options; or you can define bean(s) of type org.apache.activemq.artemis.jms.server.config.JMSQueueConfiguration or org.apache.activemq.artemis.jms.server.config.TopicConfiguration, for advanced queue and topic configurations respectively.

See {sc-spring-boot-autoconfigure}/jms/artemis/ArtemisProperties.{sc-ext}[ArtemisProperties] for more of the supported options.

No JNDI lookup is involved at all and destinations are resolved against their names, either using the ‘name’ attribute in the Artemis configuration or the names provided through configuration.

Using a JNDI ConnectionFactory

If you are running your application in an Application Server Spring Boot will attempt to locate a JMS ConnectionFactory using JNDI. By default the locations java:/JmsXA and java:/XAConnectionFactory will be checked. You can use the spring.jms.jndi-name property if you need to specify an alternative location:

spring.jms.jndi-name=java:/MyConnectionFactory

Sending a message

Spring’s JmsTemplate is auto-configured and you can autowire it directly into your own beans:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jms.core.JmsTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

	private final JmsTemplate jmsTemplate;

	@Autowired
	public MyBean(JmsTemplate jmsTemplate) {
		this.jmsTemplate = jmsTemplate;
	}

	// ...

}

Note	{spring-javadoc}/jms/core/JmsMessagingTemplate.{dc-ext}[JmsMessagingTemplate] can be injected in a similar manner. If a DestinationResolver or MessageConverter beans are defined, they are associated automatically to the auto-configured JmsTemplate.

Receiving a message

When the JMS infrastructure is present, any bean can be annotated with @JmsListener to create a listener endpoint. If no JmsListenerContainerFactory has been defined, a default one is configured automatically. If a DestinationResolver or MessageConverter beans are defined, they are associated automatically to the default factory.

The default factory is transactional by default. If you are running in an infrastructure where a JtaTransactionManager is present, it will be associated to the listener container by default. If not, the sessionTransacted flag will be enabled. In that latter scenario, you can associate your local data store transaction to the processing of an incoming message by adding @Transactional on your listener method (or a delegate thereof). This will make sure that the incoming message is acknowledged once the local transaction has completed. This also includes sending response messages that have been performed on the same JMS session.

The following component creates a listener endpoint on the someQueue destination:

@Component
public class MyBean {

	@JmsListener(destination = "someQueue")
	public void processMessage(String content) {
		// ...
	}

}

Tip	Check {spring-javadoc}/jms/annotation/EnableJms.{dc-ext}[the Javadoc of @EnableJms] for more details.

If you need to create more JmsListenerContainerFactory instances or if you want to override the default, Spring Boot provides a DefaultJmsListenerContainerFactoryConfigurer that you can use to initialize a DefaultJmsListenerContainerFactory with the same settings as the one that is auto-configured.

For instance, the following exposes another factory that uses a specific MessageConverter:

@Configuration
static class JmsConfiguration {

	@Bean
	public DefaultJmsListenerContainerFactory myFactory(
			DefaultJmsListenerContainerFactoryConfigurer configurer) {
		DefaultJmsListenerContainerFactory factory =
				new DefaultJmsListenerContainerFactory();
		configurer.configure(factory, connectionFactory());
		factory.setMessageConverter(myMessageConverter());
		return factory;
	}

}

Then you can use in any @JmsListener-annotated method as follows:

@Component
public class MyBean {

	@JmsListener(destination = "someQueue", containerFactory="myFactory")
	public void processMessage(String content) {
		// ...
	}

}

AMQP

The Advanced Message Queuing Protocol (AMQP) is a platform-neutral, wire-level protocol for message-oriented middleware. The Spring AMQP project applies core Spring concepts to the development of AMQP-based messaging solutions. Spring Boot offers several conveniences for working with AMQP via RabbitMQ, including the spring-boot-starter-amqp ‘Starter’.

RabbitMQ support

RabbitMQ is a lightweight, reliable, scalable and portable message broker based on the AMQP protocol. Spring uses RabbitMQ to communicate using the AMQP protocol.

RabbitMQ configuration is controlled by external configuration properties in spring.rabbitmq.*. For example, you might declare the following section in application.properties:

spring.rabbitmq.host=localhost
spring.rabbitmq.port=5672
spring.rabbitmq.username=admin
spring.rabbitmq.password=secret

See {sc-spring-boot-autoconfigure}/amqp/RabbitProperties.{sc-ext}[RabbitProperties] for more of the supported options.

Tip	Check Understanding AMQP, the protocol used by RabbitMQ for more details.

Sending a message

Spring’s AmqpTemplate and AmqpAdmin are auto-configured and you can autowire them directly into your own beans:

import org.springframework.amqp.core.AmqpAdmin;
import org.springframework.amqp.core.AmqpTemplate;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

	private final AmqpAdmin amqpAdmin;
	private final AmqpTemplate amqpTemplate;

	@Autowired
	public MyBean(AmqpAdmin amqpAdmin, AmqpTemplate amqpTemplate) {
		this.amqpAdmin = amqpAdmin;
		this.amqpTemplate = amqpTemplate;
	}

	// ...

}

Note	{spring-amqp-javadoc}/rabbit/core/RabbitMessagingTemplate.{dc-ext}[RabbitMessagingTemplate] can be injected in a similar manner. If a MessageConverter bean is defined, it is associated automatically to the auto-configured AmqpTemplate.

Any org.springframework.amqp.core.Queue that is defined as a bean will be automatically used to declare a corresponding queue on the RabbitMQ instance if necessary.

You can enable retries on the AmqpTemplate to retry operations, for example in the event the broker connection is lost. Retries are disabled by default.

Receiving a message

When the Rabbit infrastructure is present, any bean can be annotated with @RabbitListener to create a listener endpoint. If no RabbitListenerContainerFactory has been defined, a default SimpleRabbitListenerContainerFactory is configured automatically and you can switch to a direct container using the spring.rabbitmq.listener.type property. If a MessageConverter or MessageRecoverer beans are defined, they are associated automatically to the default factory.

The following component creates a listener endpoint on the someQueue queue:

@Component
public class MyBean {

	@RabbitListener(queues = "someQueue")
	public void processMessage(String content) {
		// ...
	}

}

Tip	Check {spring-amqp-javadoc}/rabbit/annotation/EnableRabbit.{dc-ext}[the Javadoc of @EnableRabbit] for more details.

If you need to create more RabbitListenerContainerFactory instances or if you want to override the default, Spring Boot provides a SimpleRabbitListenerContainerFactoryConfigurer and DirectRabbitListenerContainerFactoryConfigurer that you can use to initialize a SimpleRabbitListenerContainerFactory and DirectRabbitListenerContainerFactory with the same settings as the one used by the auto-configuration.

Tip	It doesn’t matter which container type you’ve chosen, those two beans are exposed by the auto-configuration.

For instance, the following exposes another factory that uses a specific MessageConverter:

@Configuration
static class RabbitConfiguration {

	@Bean
	public SimpleRabbitListenerContainerFactory myFactory(
			SimpleRabbitListenerContainerFactoryConfigurer configurer) {
		SimpleRabbitListenerContainerFactory factory =
				new SimpleRabbitListenerContainerFactory();
		configurer.configure(factory, connectionFactory);
		factory.setMessageConverter(myMessageConverter());
		return factory;
	}

}

Then you can use in any @RabbitListener-annotated method as follows:

@Component
public class MyBean {

	@RabbitListener(queues = "someQueue", containerFactory="myFactory")
	public void processMessage(String content) {
		// ...
	}

}

You can enable retries to handle situations where your listener throws an exception. By default RejectAndDontRequeueRecoverer is used but you can define a MessageRecoverer of your own. When retries are exhausted, the message will be rejected and either dropped or routed to a dead-letter exchange if the broker is configured so. Retries are disabled by default.

Important

If retries are not enabled and the listener throws an exception, by default the delivery will be retried indefinitely. You can modify this behavior in two ways; set the defaultRequeueRejected property to false and zero re-deliveries will be attempted; or, throw an AmqpRejectAndDontRequeueException to signal the message should be rejected. This is the mechanism used when retries are enabled and the maximum delivery attempts are reached.

Apache Kafka Support

Apache Kafka is supported by providing auto-configuration of the spring-kafka project.

Kafka configuration is controlled by external configuration properties in spring.kafka.*. For example, you might declare the following section in application.properties:

spring.kafka.bootstrap-servers=localhost:9092
spring.kafka.consumer.group-id=myGroup

See {sc-spring-boot-autoconfigure}/kafka/KafkaProperties.{sc-ext}[KafkaProperties] for more of the supported options.

Sending a Message

Spring’s KafkaTemplate is auto-configured and you can autowire them directly in your own beans:

@Component
public class MyBean {

	private final KafkaTemplate kafkaTemplate;

	@Autowired
	public MyBean(KafkaTemplate kafkaTemplate) {
		this.kafkaTemplate = kafkaTemplate;
	}

	// ...

}

Receiving a Message

When the Apache Kafka infrastructure is present, any bean can be annotated with @KafkaListener to create a listener endpoint. If no KafkaListenerContainerFactory has been defined, a default one is configured automatically with keys defined in spring.kafka.listener.*.

The following component creates a listener endpoint on the someTopic topic:

@Component
public class MyBean {

	@KafkaListener(topics = "someTopic")
	public void processMessage(String content) {
		// ...
	}

}

Additional Kafka Properties

The properties supported by auto configuration are shown in [common-application-properties]. Note that these properties (hyphenated or camelCase) map directly to the Apache Kafka dotted properties for the most part, refer to the Apache Kafka documentation for details.

The first few of these properties apply to both producers and consumers, but can be specified at the producer or consumer level if you wish to use different values for each. Apache Kafka designates properties with an importance: HIGH, MEDIUM and LOW. Spring Boot auto configuration supports all HIGH importance properties, some selected MEDIUM and LOW, and any that do not have a default value.

Only a subset of the properties supported by Kafka are available via the KafkaProperties class. If you wish to configure the producer or consumer with additional properties that are not directly supported, use the following:

spring.kafka.properties.foo.bar=baz

This sets the common foo.bar Kafka property to baz.

These properties will be shared by both the consumer and producer factory beans. If you wish to customize these components with different properties, such as to use a different metrics reader for each, you can override the bean definitions, as follows:

link:{code-examples}/kafka/KafkaSpecialProducerConsumerConfigExample.java[role=include]

Calling REST services

If you need to call remote REST services from your application, you can use Spring Framework’s RestTemplate class. Since RestTemplate instances often need to be customized before being used, Spring Boot does not provide any single auto-configured RestTemplate bean. It does, however, auto-configure a RestTemplateBuilder which can be used to create RestTemplate instances when needed. The auto-configured RestTemplateBuilder will ensure that sensible HttpMessageConverters are applied to RestTemplate instances.

Here’s a typical example:

@Service
public class MyBean {

	private final RestTemplate restTemplate;

	public MyBean(RestTemplateBuilder restTemplateBuilder) {
		this.restTemplate = restTemplateBuilder.build();
	}

	public Details someRestCall(String name) {
		return this.restTemplate.getForObject("/{name}/details", Details.class, name);
	}

}

Tip	RestTemplateBuilder includes a number of useful methods that can be used to quickly configure a RestTemplate. For example, to add BASIC auth support you can use builder.basicAuthorization("user", "password").build().

RestTemplate customization

There are three main approaches to RestTemplate customization, depending on how broadly you want the customizations to apply.

To make the scope of any customizations as narrow as possible, inject the auto-configured RestTemplateBuilder and then call its methods as required. Each method call returns a new RestTemplateBuilder instance so the customizations will only affect this use of the builder.

To make an application-wide, additive customization a RestTemplateCustomizer bean can be used. All such beans are automatically registered with the auto-configured RestTemplateBuilder and will be applied to any templates that are built with it.

Here’s an example of a customizer that configures the use of a proxy for all hosts except 192.168.0.5:

link:{code-examples}/web/client/RestTemplateProxyCustomizationExample.java[role=include]

Lastly, the most extreme (and rarely used) option is to create your own RestTemplateBuilder bean. This will switch off the auto-configuration of a RestTemplateBuilder and will prevent any RestTemplateCustomizer beans from being used.

Validation

The method validation feature supported by Bean Validation 1.1 is automatically enabled as long as a JSR-303 implementation (e.g. Hibernate validator) is on the classpath. This allows bean methods to be annotated with javax.validation constraints on their parameters and/or on their return value. Target classes with such annotated methods need to be annotated with the @Validated annotation at the type level for their methods to be searched for inline constraint annotations.

For instance, the following service triggers the validation of the first argument, making sure its size is between 8 and 10

@Service
@Validated
public class MyBean {

	public Archive findByCodeAndAuthor(@Size(min = 8, max = 10) String code,
			Author author) {
		...
	}

}

Sending email

The Spring Framework provides an easy abstraction for sending email using the JavaMailSender interface and Spring Boot provides auto-configuration for it as well as a starter module.

Tip	Check the {spring-reference}/#mail[reference documentation] for a detailed explanation of how you can use JavaMailSender.

If spring.mail.host and the relevant libraries (as defined by spring-boot-starter-mail) are available, a default JavaMailSender is created if none exists. The sender can be further customized by configuration items from the spring.mail namespace, see the {sc-spring-boot-autoconfigure}/mail/MailProperties.{sc-ext}[MailProperties] for more details.

In particular, certain default timeout values are infinite and you may want to change that to avoid having a thread blocked by an unresponsive mail server:

spring.mail.properties.mail.smtp.connectiontimeout=5000
spring.mail.properties.mail.smtp.timeout=3000
spring.mail.properties.mail.smtp.writetimeout=5000

Distributed Transactions with JTA

Spring Boot supports distributed JTA transactions across multiple XA resources using either an Atomikos or Bitronix embedded transaction manager. JTA transactions are also supported when deploying to a suitable Java EE Application Server.

When a JTA environment is detected, Spring’s JtaTransactionManager will be used to manage transactions. Auto-configured JMS, DataSource and JPA beans will be upgraded to support XA transactions. You can use standard Spring idioms such as @Transactional to participate in a distributed transaction. If you are within a JTA environment and still want to use local transactions you can set the spring.jta.enabled property to false to disable the JTA auto-configuration.

Using an Atomikos transaction manager

Atomikos is a popular open source transaction manager which can be embedded into your Spring Boot application. You can use the spring-boot-starter-jta-atomikos Starter to pull in the appropriate Atomikos libraries. Spring Boot will auto-configure Atomikos and ensure that appropriate depends-on settings are applied to your Spring beans for correct startup and shutdown ordering.

By default Atomikos transaction logs will be written to a transaction-logs directory in your application home directory (the directory in which your application jar file resides). You can customize this directory by setting a spring.jta.log-dir property in your application.properties file. Properties starting spring.jta.atomikos.properties can also be used to customize the Atomikos UserTransactionServiceImp. See the {dc-spring-boot}/jta/atomikos/AtomikosProperties.{dc-ext}[AtomikosProperties Javadoc] for complete details.

Note

To ensure that multiple transaction managers can safely coordinate the same resource managers, each Atomikos instance must be configured with a unique ID. By default this ID is the IP address of the machine on which Atomikos is running. To ensure uniqueness in production, you should configure the spring.jta.transaction-manager-id property with a different value for each instance of your application.

Using a Bitronix transaction manager

Bitronix is popular open source JTA transaction manager implementation. You can use the spring-boot-starter-jta-bitronix starter to add the appropriate Bitronix dependencies to your project. As with Atomikos, Spring Boot will automatically configure Bitronix and post-process your beans to ensure that startup and shutdown ordering is correct.

By default Bitronix transaction log files (part1.btm and part2.btm) will be written to a transaction-logs directory in your application home directory. You can customize this directory by using the spring.jta.log-dir property. Properties starting spring.jta.bitronix.properties are also bound to the bitronix.tm.Configuration bean, allowing for complete customization. See the Bitronix documentation for details.

Note

To ensure that multiple transaction managers can safely coordinate the same resource managers, each Bitronix instance must be configured with a unique ID. By default this ID is the IP address of the machine on which Bitronix is running. To ensure uniqueness in production, you should configure the spring.jta.transaction-manager-id property with a different value for each instance of your application.

Using a Narayana transaction manager

Narayana is popular open source JTA transaction manager implementation supported by JBoss. You can use the spring-boot-starter-jta-narayana starter to add the appropriate Narayana dependencies to your project. As with Atomikos and Bitronix, Spring Boot will automatically configure Narayana and post-process your beans to ensure that startup and shutdown ordering is correct.

By default Narayana transaction logs will be written to a transaction-logs directory in your application home directory (the directory in which your application jar file resides). You can customize this directory by setting a spring.jta.log-dir property in your application.properties file. Properties starting spring.jta.narayana.properties can also be used to customize the Narayana configuration. See the {dc-spring-boot}/jta/narayana/NarayanaProperties.{dc-ext}[NarayanaProperties Javadoc] for complete details.

Note

To ensure that multiple transaction managers can safely coordinate the same resource managers, each Narayana instance must be configured with a unique ID. By default this ID is set to 1. To ensure uniqueness in production, you should configure the spring.jta.transaction-manager-id property with a different value for each instance of your application.

Using a Java EE managed transaction manager

If you are packaging your Spring Boot application as a war or ear file and deploying it to a Java EE application server, you can use your application servers built-in transaction manager. Spring Boot will attempt to auto-configure a transaction manager by looking at common JNDI locations (java:comp/UserTransaction, java:comp/TransactionManager etc). If you are using a transaction service provided by your application server, you will generally also want to ensure that all resources are managed by the server and exposed over JNDI. Spring Boot will attempt to auto-configure JMS by looking for a ConnectionFactory at the JNDI path java:/JmsXA or java:/XAConnectionFactory and you can use the spring.datasource.jndi-name property to configure your DataSource.

Mixing XA and non-XA JMS connections

When using JTA, the primary JMS ConnectionFactory bean will be XA aware and participate in distributed transactions. In some situations you might want to process certain JMS messages using a non-XA ConnectionFactory. For example, your JMS processing logic might take longer than the XA timeout.

If you want to use a non-XA ConnectionFactory you can inject the nonXaJmsConnectionFactory bean rather than the @Primary jmsConnectionFactory bean. For consistency the jmsConnectionFactory bean is also provided using the bean alias xaJmsConnectionFactory.

For example:

// Inject the primary (XA aware) ConnectionFactory
@Autowired
private ConnectionFactory defaultConnectionFactory;

// Inject the XA aware ConnectionFactory (uses the alias and injects the same as above)
@Autowired
@Qualifier("xaJmsConnectionFactory")
private ConnectionFactory xaConnectionFactory;

// Inject the non-XA aware ConnectionFactory
@Autowired
@Qualifier("nonXaJmsConnectionFactory")
private ConnectionFactory nonXaConnectionFactory;

Supporting an alternative embedded transaction manager

The {sc-spring-boot}/jta/XAConnectionFactoryWrapper.{sc-ext}[XAConnectionFactoryWrapper] and {sc-spring-boot}/jta/XADataSourceWrapper.{sc-ext}[XADataSourceWrapper] interfaces can be used to support alternative embedded transaction managers. The interfaces are responsible for wrapping XAConnectionFactory and XADataSource beans and exposing them as regular ConnectionFactory and DataSource beans which will transparently enroll in the distributed transaction. DataSource and JMS auto-configuration will use JTA variants as long as you have a JtaTransactionManager bean and appropriate XA wrapper beans registered within your ApplicationContext.

The {sc-spring-boot}/jta/bitronix/BitronixXAConnectionFactoryWrapper.{sc-ext}[BitronixXAConnectionFactoryWrapper] and {sc-spring-boot}/jta/bitronix/BitronixXADataSourceWrapper.{sc-ext}[BitronixXADataSourceWrapper] provide good examples of how to write XA wrappers.

Hazelcast

If hazelcast is on the classpath and a suitable configuration is found, Spring Boot will auto-configure an HazelcastInstance that you can inject in your application.

You can define a com.hazelcast.config.Config bean and we’ll use that. If your configuration defines an instance name, we’ll try to locate an existing instance rather than creating a new one.

You could also specify the hazelcast.xml configuration file to use via configuration:

spring.hazelcast.config=classpath:config/my-hazelcast.xml

Otherwise, Spring Boot tries to find the Hazelcast configuration from the default locations, that is hazelcast.xml in the working directory or at the root of the classpath. We also check if the hazelcast.config system property is set. Check the Hazelcast documentation for more details.

If hazelcast-client is present on the classpath, Spring Boot will first attempt to create a client with similar rules as above, that is:

• The presence of a com.hazelcast.client.config.ClientConfig bean

• A configuration file defined by the spring.hazelcast.config property

• The presence of the hazelcast.client.config system property

• A hazelcast-client.xml in the working directory or at the root of the classpath

Note	Spring Boot also has an explicit caching support for Hazelcast. The HazelcastInstance is automatically wrapped in a CacheManager implementation if caching is enabled.

Quartz Scheduler

Spring Boot offers several conveniences for working with the Quartz scheduler, including the spring-boot-starter-quartz ‘Starter’. If Quartz is available, a Scheduler will be auto-configured (via the SchedulerFactoryBean abstraction).

Beans of the following types will be automatically picked up and associated with the the Scheduler:

• JobDetail: defines a particular Job. JobDetail instance can easily be built with the JobBuilder API

• Calendar

• Trigger: defines when a particular job is triggered

By default, an in-memory JobStore will be used. However, it is possible to configure a JDBC-based store if a DataSource bean is available in your application and if the spring.quartz.job-store-type property is configured accordingly:

spring.quartz.job-store-type=jdbc

When the jdbc store is used, the schema can be initialized on startup:

spring.quartz.jdbc.initialize-schema=true

Note	The database is detected by default and initialized using the standard scripts provided with the Quartz library. It is also possible to provide a custom script using the spring.quartz.jdbc.schema property.

Quartz Scheduler configuration can be customized using Quartz configuration properties (see spring.quartz.properties.*) and SchedulerFactoryBeanCustomizer beans which allows programmatic SchedulerFactoryBean customization.

Job can define setters to inject data map properties. Regular beans can also be injected in a similar manner:

public class SampleJob extends QuartzJobBean {

	private MyService myService;
	private String name;

	// Inject "MyService" bean
	public void setMyService(MyService myService) { ... }

	// Inject the "name" job data property
	public void setName(String name) { ... }

	@Override
	protected void executeInternal(JobExecutionContext context)
			throws JobExecutionException {
		...
	}

}

Spring Integration

Spring Boot offers several conveniences for working with Spring Integration, including the spring-boot-starter-integration ‘Starter’. Spring Integration provides abstractions over messaging and also other transports such as HTTP, TCP etc. If Spring Integration is available on your classpath it will be initialized through the @EnableIntegration annotation.

Spring Boot will also configure some features that are triggered by the presence of additional Spring Integration modules. Message processing statistics will be published over JMX if 'spring-integration-jmx' is also on the classpath. If 'spring-integration-jdbc' is available, the default database schema can be created on startup:

spring.integration.jdbc.initializer.enabled=true

See the {sc-spring-boot-autoconfigure}/integration/IntegrationAutoConfiguration.{sc-ext}[IntegrationAutoConfiguration] and {sc-spring-boot-autoconfigure}/integration/IntegrationProperties.{sc-ext}[IntegrationProperties] classes for more details.

Spring Session

Spring Boot provides Spring Session auto-configuration for a wide range of stores:

• JDBC

• Redis

• Hazelcast

• HashMap

If Spring Session is available, you must choose the {sc-spring-boot-autoconfigure}/session/StoreType.{sc-ext}[StoreType] that you wish to use to store the sessions. For instance to use JDBC as backend store, you’d configure your application as follows:

spring.session.store-type=jdbc

Tip	You can disable Spring Session by setting the store-type to none.

Each store has specific additional settings. For instance it is possible to customize the name of the table for the jdbc store:

spring.session.jdbc.table-name=SESSIONS

Monitoring and management over JMX

Java Management Extensions (JMX) provide a standard mechanism to monitor and manage applications. By default Spring Boot will create an MBeanServer with bean id ‘mbeanServer’ and expose any of your beans that are annotated with Spring JMX annotations (@ManagedResource, @ManagedAttribute, @ManagedOperation).

See the {sc-spring-boot-autoconfigure}/jmx/JmxAutoConfiguration.{sc-ext}[JmxAutoConfiguration] class for more details.

Testing

Spring Boot provides a number of utilities and annotations to help when testing your application. Test support is provided by two modules; spring-boot-test contains core items, and spring-boot-test-autoconfigure supports auto-configuration for tests.

Most developers will just use the spring-boot-starter-test ‘Starter’ which imports both Spring Boot test modules as well has JUnit, AssertJ, Hamcrest and a number of other useful libraries.

Test scope dependencies

If you use the spring-boot-starter-test ‘Starter’ (in the test scope), you will find the following provided libraries:

• JUnit — The de-facto standard for unit testing Java applications.

• {spring-reference}/#integration-testing[Spring Test] & Spring Boot Test — Utilities and integration test support for Spring Boot applications.

• AssertJ — A fluent assertion library.

• Hamcrest — A library of matcher objects (also known as constraints or predicates).

• Mockito — A Java mocking framework.

• JSONassert — An assertion library for JSON.

• JsonPath — XPath for JSON.

These are common libraries that we generally find useful when writing tests. You are free to add additional test dependencies of your own if these don’t suit your needs.

Testing Spring applications

One of the major advantages of dependency injection is that it should make your code easier to unit test. You can simply instantiate objects using the new operator without even involving Spring. You can also use mock objects instead of real dependencies.

Often you need to move beyond ‘unit testing’ and start ‘integration testing’ (with a Spring ApplicationContext actually involved in the process). It’s useful to be able to perform integration testing without requiring deployment of your application or needing to connect to other infrastructure.

The Spring Framework includes a dedicated test module for just such integration testing. You can declare a dependency directly to org.springframework:spring-test or use the spring-boot-starter-test ‘Starter’ to pull it in transitively.

If you have not used the spring-test module before you should start by reading the {spring-reference}/#testing[relevant section] of the Spring Framework reference documentation.

Testing Spring Boot applications

A Spring Boot application is just a Spring ApplicationContext, so nothing very special has to be done to test it beyond what you would normally do with a vanilla Spring context. One thing to watch out for though is that the external properties, logging and other features of Spring Boot are only installed in the context by default if you use SpringApplication to create it.

Spring Boot provides a @SpringBootTest annotation which can be used as an alternative to the standard spring-test @ContextConfiguration annotation when you need Spring Boot features. The annotation works by creating the ApplicationContext used in your tests via SpringApplication.

You can use the webEnvironment attribute of @SpringBootTest to further refine how your tests will run:

• MOCK — Loads a WebApplicationContext and provides a mock servlet environment. Embedded servlet containers are not started when using this annotation. If servlet APIs are not on your classpath this mode will transparently fallback to creating a regular non-web ApplicationContext. Can be used in conjunction with @AutoConfigureMockMvc for MockMvc-based testing of your application.

• RANDOM_PORT — Loads an ServletWebServerApplicationContext and provides a real servlet environment. Embedded servlet containers are started and listening on a random port.

• DEFINED_PORT — Loads an ServletWebServerApplicationContext and provides a real servlet environment. Embedded servlet containers are started and listening on a defined port (i.e from your application.properties or on the default port 8080).

• NONE — Loads an ApplicationContext using SpringApplication but does not provide any servlet environment (mock or otherwise).

Note

If your test is @Transactional, it will rollback the transaction at the end of each test method by default. If you’re using this arrangement in combination with either RANDOM_PORT or DEFINED_PORT, any transaction initiated on the server won’t rollback as the test is running in a different thread than the server processing.

Note	In addition to @SpringBootTest a number of other annotations are also provided for testing more specific slices of an application. See below for details.

Tip	Don’t forget to also add @RunWith(SpringRunner.class) to your test, otherwise the annotations will be ignored.

Detecting test configuration

If you’re familiar with the Spring Test Framework, you may be used to using @ContextConfiguration(classes=…​) in order to specify which Spring @Configuration to load. Alternatively, you might have often used nested @Configuration classes within your test.

When testing Spring Boot applications this is often not required. Spring Boot’s @*Test annotations will search for your primary configuration automatically whenever you don’t explicitly define one.

The search algorithm works up from the package that contains the test until it finds a @SpringBootApplication or @SpringBootConfiguration annotated class. As long as you’ve structured your code in a sensible way your main configuration is usually found.

If you want to customize the primary configuration, you can use a nested @TestConfiguration class. Unlike a nested @Configuration class which would be used instead of a your application’s primary configuration, a nested @TestConfiguration class will be used in addition to your application’s primary configuration.

Note	Spring’s test framework will cache application contexts between tests. Therefore, as long as your tests share the same configuration (no matter how it’s discovered), the potentially time consuming process of loading the context will only happen once.

Excluding test configuration

If your application uses component scanning, for example if you use @SpringBootApplication or @ComponentScan, you may find top-level configuration classes created only for specific tests accidentally get picked up everywhere.

As we have seen above, @TestConfiguration can be used on an inner class of a test to customize the primary configuration. When placed on a top-level class, @TestConfiguration indicates that classes in src/test/java should not be picked up by scanning. You can then import that class explicitly where it is required:

@RunWith(SpringRunner.class)
@SpringBootTest
@Import(MyTestsConfiguration.class)
public class MyTests {

	@Test
	public void exampleTest() {
		...
	}

}

Note	If you directly use @ComponentScan (i.e. not via @SpringBootApplication) you will need to register the TypeExcludeFilter with it. See {dc-spring-boot}/context/TypeExcludeFilter.{dc-ext}[the Javadoc] for details.

Working with random ports

If you need to start a full running server for tests, we recommend that you use random ports. If you use @SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT) an available port will be picked at random each time your test runs.

The @LocalServerPort annotation can be used to inject the actual port used into your test. For convenience, tests that need to make REST calls to the started server can additionally @Autowire a TestRestTemplate which will resolve relative links to the running server.

link:{code-examples}/test/web/RandomPortExampleTests.java[role=include]

Mocking and spying beans

It’s sometimes necessary to mock certain components within your application context when running tests. For example, you may have a facade over some remote service that’s unavailable during development. Mocking can also be useful when you want to simulate failures that might be hard to trigger in a real environment.

Spring Boot includes a @MockBean annotation that can be used to define a Mockito mock for a bean inside your ApplicationContext. You can use the annotation to add new beans, or replace a single existing bean definition. The annotation can be used directly on test classes, on fields within your test, or on @Configuration classes and fields. When used on a field, the instance of the created mock will also be injected. Mock beans are automatically reset after each test method.

Here’s a typical example where we replace an existing RemoteService bean with a mock implementation:

import org.junit.*;
import org.junit.runner.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.context.*;
import org.springframework.boot.test.mock.mockito.*;
import org.springframework.test.context.junit4.*;

import static org.assertj.core.api.Assertions.*;
import static org.mockito.BDDMockito.*;

@RunWith(SpringRunner.class)
@SpringBootTest
public class MyTests {

	@MockBean
	private RemoteService remoteService;

	@Autowired
	private Reverser reverser;

	@Test
	public void exampleTest() {
		// RemoteService has been injected into the reverser bean
		given(this.remoteService.someCall()).willReturn("mock");
		String reverse = reverser.reverseSomeCall();
		assertThat(reverse).isEqualTo("kcom");
	}

}

Additionally you can also use @SpyBean to wrap any existing bean with a Mockito spy. See the Javadoc for full details.

Auto-configured tests

Spring Boot’s auto-configuration system works well for applications, but can sometimes be a little too much for tests. It’s often helpful to load only the parts of the configuration that are required to test a ‘slice’ of your application. For example, you might want to test that Spring MVC controllers are mapping URLs correctly, and you don’t want to involve database calls in those tests; or you might be wanting to test JPA entities, and you’re not interested in web layer when those tests run.

The spring-boot-test-autoconfigure module includes a number of annotations that can be used to automatically configure such ‘slices’. Each of them works in a similar way, providing a @…​Test annotation that loads the ApplicationContext and one or more @AutoConfigure…​ annotations that can be used to customize auto-configuration settings.

Note	Each slice loads a very restricted set of auto-configuration classes. If you need to exclude one of them, most @…​Test annotations provide an excludeAutoConfiguration attribute. Alternatively, you can use @ImportAutoConfiguration#exclude.

Tip	It’s also possible to use the @AutoConfigure…​ annotations with the standard @SpringBootTest annotation. You can use this combination if you’re not interested in ‘slicing’ your application but you want some of the auto-configured test beans.

Auto-configured JSON tests

To test that Object JSON serialization and deserialization is working as expected you can use the @JsonTest annotation. @JsonTest will auto-configure Jackson ObjectMapper, any @JsonComponent beans and any Jackson Modules. It also configures Gson if you happen to be using that instead of, or as well as, Jackson. If you need to configure elements of the auto-configuration you can use the @AutoConfigureJsonTesters annotation.

Spring Boot includes AssertJ based helpers that work with the JSONassert and JsonPath libraries to check that JSON is as expected. The JacksonTester, GsonTester and BasicJsonTester classes can be used for Jackson, Gson and Strings respectively. Any helper fields on the test class can be @Autowired when using @JsonTest.

import org.junit.*;
import org.junit.runner.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.autoconfigure.json.*;
import org.springframework.boot.test.context.*;
import org.springframework.boot.test.json.*;
import org.springframework.test.context.junit4.*;

import static org.assertj.core.api.Assertions.*;

@RunWith(SpringRunner.class)
@JsonTest
public class MyJsonTests {

	@Autowired
	private JacksonTester<VehicleDetails> json;

	@Test
	public void testSerialize() throws Exception {
		VehicleDetails details = new VehicleDetails("Honda", "Civic");
		// Assert against a `.json` file in the same package as the test
		assertThat(this.json.write(details)).isEqualToJson("expected.json");
		// Or use JSON path based assertions
		assertThat(this.json.write(details)).hasJsonPathStringValue("@.make");
		assertThat(this.json.write(details)).extractingJsonPathStringValue("@.make")
				.isEqualTo("Honda");
	}

	@Test
	public void testDeserialize() throws Exception {
		String content = "{\"make\":\"Ford\",\"model\":\"Focus\"}";
		assertThat(this.json.parse(content))
				.isEqualTo(new VehicleDetails("Ford", "Focus"));
		assertThat(this.json.parseObject(content).getMake()).isEqualTo("Ford");
	}

}

Note	JSON helper classes can also be used directly in standard unit tests. Simply call the initFields method of the helper in your @Before method if you aren’t using @JsonTest.

A list of the auto-configuration that is enabled by @JsonTest can be found in the appendix.

Auto-configured Spring MVC tests

To test Spring MVC controllers are working as expected you can use the @WebMvcTest annotation. @WebMvcTest will auto-configure the Spring MVC infrastructure and limit scanned beans to @Controller, @ControllerAdvice, @JsonComponent, Filter, WebMvcConfigurer and HandlerMethodArgumentResolver. Regular @Component beans will not be scanned when using this annotation.

Often @WebMvcTest will be limited to a single controller and used in combination with @MockBean to provide mock implementations for required collaborators.

@WebMvcTest also auto-configures MockMvc. Mock MVC offers a powerful way to quickly test MVC controllers without needing to start a full HTTP server.

Tip	You can also auto-configure MockMvc in a non-@WebMvcTest (e.g. SpringBootTest) by annotating it with @AutoConfigureMockMvc.

import org.junit.*;
import org.junit.runner.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.autoconfigure.web.servlet.*;
import org.springframework.boot.test.mock.mockito.*;

import static org.assertj.core.api.Assertions.*;
import static org.mockito.BDDMockito.*;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

@RunWith(SpringRunner.class)
@WebMvcTest(UserVehicleController.class)
public class MyControllerTests {

	@Autowired
	private MockMvc mvc;

	@MockBean
	private UserVehicleService userVehicleService;

	@Test
	public void testExample() throws Exception {
		given(this.userVehicleService.getVehicleDetails("sboot"))
				.willReturn(new VehicleDetails("Honda", "Civic"));
		this.mvc.perform(get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
				.andExpect(status().isOk()).andExpect(content().string("Honda Civic"));
	}

}

Tip	If you need to configure elements of the auto-configuration (for example when servlet filters should be applied) you can use attributes in the @AutoConfigureMockMvc annotation.

If you use HtmlUnit or Selenium, auto-configuration will also provide a WebClient bean and/or a WebDriver bean. Here is an example that uses HtmlUnit:

import com.gargoylesoftware.htmlunit.*;
import org.junit.*;
import org.junit.runner.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.autoconfigure.web.servlet.*;
import org.springframework.boot.test.mock.mockito.*;

import static org.assertj.core.api.Assertions.*;
import static org.mockito.BDDMockito.*;

@RunWith(SpringRunner.class)
@WebMvcTest(UserVehicleController.class)
public class MyHtmlUnitTests {

	@Autowired
	private WebClient webClient;

	@MockBean
	private UserVehicleService userVehicleService;

	@Test
	public void testExample() throws Exception {
		given(this.userVehicleService.getVehicleDetails("sboot"))
				.willReturn(new VehicleDetails("Honda", "Civic"));
		HtmlPage page = this.webClient.getPage("/sboot/vehicle.html");
		assertThat(page.getBody().getTextContent()).isEqualTo("Honda Civic");
	}

}

Note	By default Spring Boot will put WebDriver beans in a special “scope” to ensure that the driver is quit after each test, and that a new instance is injected. If you don’t want this behavior you can add @Scope("singleton") to your WebDriver @Bean definition.

A list of the auto-configuration that is enabled by @WebMvcTest can be found in the appendix.

Auto-configured Data JPA tests

@DataJpaTest can be used if you want to test JPA applications. By default it will configure an in-memory embedded database, scan for @Entity classes and configure Spring Data JPA repositories. Regular @Component beans will not be loaded into the ApplicationContext.

Data JPA tests are transactional and rollback at the end of each test by default, see the {spring-reference}#testcontext-tx-enabling-transactions[relevant section] in the Spring Reference Documentation for more details. If that’s not what you want, you can disable transaction management for a test or for the whole class as follows:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

@RunWith(SpringRunner.class)
@DataJpaTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
public class ExampleNonTransactionalTests {

}

Data JPA tests may also inject a {sc-spring-boot-test-autoconfigure}/orm/jpa/TestEntityManager.{sc-ext}[TestEntityManager] bean which provides an alternative to the standard JPA EntityManager specifically designed for tests. If you want to use TestEntityManager outside of @DataJpaTests you can also use the @AutoConfigureTestEntityManager annotation. A JdbcTemplate is also available if you need that.

import org.junit.*;
import org.junit.runner.*;
import org.springframework.boot.test.autoconfigure.orm.jpa.*;

import static org.assertj.core.api.Assertions.*;

@RunWith(SpringRunner.class)
@DataJpaTest
public class ExampleRepositoryTests {

	@Autowired
	private TestEntityManager entityManager;

	@Autowired
	private UserRepository repository;

	@Test
	public void testExample() throws Exception {
		this.entityManager.persist(new User("sboot", "1234"));
		User user = this.repository.findByUsername("sboot");
		assertThat(user.getUsername()).isEqualTo("sboot");
		assertThat(user.getVin()).isEqualTo("1234");
	}

}

In-memory embedded databases generally work well for tests since they are fast and don’t require any developer installation. If, however, you prefer to run tests against a real database you can use the @AutoConfigureTestDatabase annotation:

@RunWith(SpringRunner.class)
@DataJpaTest
@AutoConfigureTestDatabase(replace=Replace.NONE)
public class ExampleRepositoryTests {

	// ...

}

A list of the auto-configuration that is enabled by @DataJpaTest can be found in the appendix.

Auto-configured JDBC tests

@JdbcTest is similar to @DataJpaTest but for pure jdbc-related tests. By default it will also configure an in-memory embedded database and a JdbcTemplate. Regular @Component beans will not be loaded into the ApplicationContext.

JDBC tests are transactional and rollback at the end of each test by default, see the {spring-reference}#testcontext-tx-enabling-transactions[relevant section] in the Spring Reference Documentation for more details. If that’s not what you want, you can disable transaction management for a test or for the whole class as follows:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.autoconfigure.jdbc.JdbcTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

@RunWith(SpringRunner.class)
@JdbcTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
public class ExampleNonTransactionalTests {

}

If you prefer your test to run against a real database, you can use the @AutoConfigureTestDatabase annotation the same way as for DataJpaTest.

A list of the auto-configuration that is enabled by @JdbcTest can be found in the appendix.

Auto-configured jOOQ tests

@JooqTest can be used in a similar fashion as @JdbcTest but for jOOQ related tests. As jOOQ relies heavily on a Java-based schema that corresponds with the database schema, the existing DataSource will be used. If you want to replace it by an in-memory database you can use @AutoconfigureTestDatabase to override those settings.

@JooqTest will configure a DSLContext. Regular @Component beans will not be loaded into the ApplicationContext:

import org.jooq.DSLContext;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.autoconfigure.jooq.JooqTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@JooqTest
public class ExampleJooqTests {

	@Autowired
	private DSLContext dslContext;
}

JOOQ tests are transactional and rollback at the end of each test by default. If that’s not what you want, you can disable transaction management for a test or for the whole test class as shown in the example above.

A list of the auto-configuration that is enabled by @JooqTest can be found in the appendix.

Auto-configured Data MongoDB tests

@DataMongoTest can be used if you want to test MongoDB applications. By default, it will configure an in-memory embedded MongoDB (if available), configure a MongoTemplate, scan for @Document classes and configure Spring Data MongoDB repositories. Regular @Component beans will not be loaded into the ApplicationContext:

import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataMongoTest
public class ExampleDataMongoTests {

	@Autowired
	private MongoTemplate mongoTemplate;

	//
}

In-memory embedded MongoDB generally works well for tests since it is fast and doesn’t require any developer installation. If, however, you prefer to run tests against a real MongoDB server you should exclude the embedded MongoDB auto-configuration:

import org.junit.runner.RunWith;
   import org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration;
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataMongoTest(excludeAutoConfiguration = EmbeddedMongoAutoConfiguration.class)
public class ExampleDataMongoNonEmbeddedTests {

}

A list of the auto-configuration that is enabled by @DataMongoTest can be found in the appendix.

Auto-configured Data Neo4j tests

@DataNeo4jTest can be used if you want to test Neo4j applications. By default, it will use an in-memory embedded Neo4j (if the embedded driver is available), scan for @NodeEntity classes and configure Spring Data Neo4j repositories. Regular @Component beans will not be loaded into the ApplicationContext:

import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataNeo4jTest
public class ExampleDataNeo4jTests {

	@Autowired
	private YourRepository repository;

	//
}

Data Neo4j tests are transactional and rollback at the end of each test by default, see the {spring-reference}#testcontext-tx-enabling-transactions[relevant section] in the Spring Reference Documentation for more details. If that’s not what you want, you can disable transaction management for a test or for the whole class as follows:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

@RunWith(SpringRunner.class)
@DataNeo4jTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
public class ExampleNonTransactionalTests {

}

A list of the auto-configuration that is enabled by @DataNeo4jTest can be found in the appendix.

Auto-configured Data LDAP tests

@DataLdapTest can be used if you want to test LDAP applications. By default, it will configure an in-memory embedded LDAP (if available), a LdapTemplate, scan for @Entry classes and configure Spring Data LDAP repositories. Regular @Component beans will not be loaded into the ApplicationContext:

import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;
import org.springframework.ldap.core.LdapTemplate;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataLdapTest
public class ExampleDataLdapTests {

	@Autowired
	private LdapTemplate ldapTemplate;

	//
}

In-memory embedded LDAP generally works well for tests since it is fast and doesn’t require any developer installation. If, however, you prefer to run tests against a real LDAP server you should exclude the embedded LDAP auto-configuration:

import org.junit.runner.RunWith;
   import org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration;
import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataLdapTest(excludeAutoConfiguration = EmbeddedLdapAutoConfiguration.class)
public class ExampleDataLdapNonEmbeddedTests {

}

A list of the auto-configuration that is enabled by @DataLdapTest can be found in the appendix.

Auto-configured REST clients

The @RestClientTest annotation can be used if you want to test REST clients. By default it will auto-configure Jackson and GSON support, configure a RestTemplateBuilder and add support for MockRestServiceServer. The specific beans that you want to test should be specified using value or components attribute of @RestClientTest:

@RunWith(SpringRunner.class)
@RestClientTest(RemoteVehicleDetailsService.class)
public class ExampleRestClientTest {

	@Autowired
	private RemoteVehicleDetailsService service;

	@Autowired
	private MockRestServiceServer server;

	@Test
	public void getVehicleDetailsWhenResultIsSuccessShouldReturnDetails()
			throws Exception {
		this.server.expect(requestTo("/greet/details"))
				.andRespond(withSuccess("hello", MediaType.TEXT_PLAIN));
		String greeting = this.service.callRestService();
		assertThat(greeting).isEqualTo("hello");
	}

}

A list of the auto-configuration that is enabled by @RestClientTest can be found in the appendix.

Auto-configured Spring REST Docs tests

The @AutoConfigureRestDocs annotation can be used if you want to use Spring REST Docs in your tests. It will automatically configure MockMvc to use Spring REST Docs and remove the need for Spring REST Docs' JUnit rule.

import org.junit.Test;
import org.junit.runner.RunWith;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.http.MediaType;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;

import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

@RunWith(SpringRunner.class)
@WebMvcTest(UserController.class)
@AutoConfigureRestDocs
public class UserDocumentationTests {

	@Autowired
	private MockMvc mvc;

	@Test
	public void listUsers() throws Exception {
		this.mvc.perform(get("/users").accept(MediaType.TEXT_PLAIN))
				.andExpect(status().isOk())
				.andDo(document("list-users"));
	}

}

@AutoConfigureRestDocs can be used to override the default output directory (target/generated-snippets if you are using Maven or build/generated-snippets if you are using Gradle). It can also be used to configure the host, scheme, and port that will appear in any documented URIs. If you require more control over Spring REST Docs' configuration a RestDocsMockMvcConfigurationCustomizer bean can be used:

@TestConfiguration
static class CustomizationConfiguration
		implements RestDocsMockMvcConfigurationCustomizer {

	@Override
	public void customize(MockMvcRestDocumentationConfigurer configurer) {
		configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
	}

}

If you want to make use of Spring REST Docs' support for a parameterized output directory, you can create a RestDocumentationResultHandler bean. The auto-configuration will call alwaysDo with this result handler, thereby causing each MockMvc call to automatically generate the default snippets:

@TestConfiguration
static class ResultHandlerConfiguration {

	@Bean
	public RestDocumentationResultHandler restDocumentation() {
		return MockMvcRestDocumentation.document("{method-name}");
	}

}

Using Spock to test Spring Boot applications

If you wish to use Spock to test a Spring Boot application you should add a dependency on Spock’s spock-spring module to your application’s build. spock-spring integrates Spring’s test framework into Spock. It is recommended that you use Spock 1.1 or later to benefit from a number of recent improvements to Spock’s Spring Framework and Spring Boot integration. Please refer to the documentation for Spock’s Spring module for further details.

Test utilities

A few test utility classes are packaged as part of spring-boot that are generally useful when testing your application.

ConfigFileApplicationContextInitializer

ConfigFileApplicationContextInitializer is an ApplicationContextInitializer that can apply to your tests to load Spring Boot application.properties files. You can use this when you don’t need the full features provided by @SpringBootTest.

@ContextConfiguration(classes = Config.class,
	initializers = ConfigFileApplicationContextInitializer.class)

Note

Using ConfigFileApplicationContextInitializer alone won’t provide support for @Value("${…​}") injection. Its only job is to ensure that application.properties files are loaded into Spring’s Environment. For @Value support you need to either additionally configure a PropertySourcesPlaceholderConfigurer or use @SpringBootTest where one will be auto-configured for you.

EnvironmentTestUtils

EnvironmentTestUtils allows you to quickly add properties to a ConfigurableEnvironment or ConfigurableApplicationContext. Simply call it with key=value strings:

EnvironmentTestUtils.addEnvironment(env, "org=Spring", "name=Boot");

OutputCapture

OutputCapture is a JUnit Rule that you can use to capture System.out and System.err output. Simply declare the capture as a @Rule then use toString() for assertions:

import org.junit.Rule;
import org.junit.Test;
import org.springframework.boot.test.rule.OutputCapture;

import static org.hamcrest.Matchers.*;
import static org.junit.Assert.*;

public class MyTest {

	@Rule
	public OutputCapture capture = new OutputCapture();

	@Test
	public void testName() throws Exception {
		System.out.println("Hello World!");
		assertThat(capture.toString(), containsString("World"));
	}

}

TestRestTemplate

TestRestTemplate is a convenience alternative to Spring’s RestTemplate that is useful in integration tests. You can get a vanilla template or one that sends Basic HTTP authentication (with a username and password). In either case the template will behave in a test-friendly way: not following redirects (so you can assert the response location), ignoring cookies (so the template is stateless), and not throwing exceptions on server-side errors. It is recommended, but not mandatory, to use Apache HTTP Client (version 4.3.2 or better), and if you have that on your classpath the TestRestTemplate will respond by configuring the client appropriately.

public class MyTest {

	private TestRestTemplate template = new TestRestTemplate();

	@Test
	public void testRequest() throws Exception {
		HttpHeaders headers = template.getForEntity("http://myhost.com", String.class).getHeaders();
		assertThat(headers.getLocation().toString(), containsString("myotherhost"));
	}

}

If you are using the @SpringBootTest annotation with WebEnvironment.RANDOM_PORT or WebEnvironment.DEFINED_PORT, you can just inject a fully configured TestRestTemplate and start using it. If necessary, additional customizations can be applied via the RestTemplateBuilder bean:

@RunWith(SpringRunner.class)
@SpringBootTest
public class MyTest {

	@Autowired
	private TestRestTemplate template;

	@Test
	public void testRequest() throws Exception {
		HttpHeaders headers = template.getForEntity("http://myhost.com", String.class).getHeaders();
		assertThat(headers.getLocation().toString(), containsString("myotherhost"));
	}

	@TestConfiguration
	static class Config {

		@Bean
		public RestTemplateBuilder restTemplateBuilder() {
			return new RestTemplateBuilder()
				.additionalMessageConverters(...)
				.customizers(...);
		}

	}

}

WebSockets

Spring Boot provides WebSockets auto-configuration for embedded Tomcat (8 and 7), Jetty 9 and Undertow. If you’re deploying a war file to a standalone container, Spring Boot assumes that the container will be responsible for the configuration of its WebSocket support.

Spring Framework provides {spring-reference}/#websocket[rich WebSocket support] that can be easily accessed via the spring-boot-starter-websocket module.

Web Services

Spring Boot provides Web Services auto-configuration so that all is required is defining your Endpoints.

The {spring-webservices-reference}[Spring Web Services features] can be easily accessed via the spring-boot-starter-webservices module.

Creating your own auto-configuration

If you work in a company that develops shared libraries, or if you work on an open-source or commercial library, you might want to develop your own auto-configuration. Auto-configuration classes can be bundled in external jars and still be picked-up by Spring Boot.

Auto-configuration can be associated to a "starter" that provides the auto-configuration code as well as the typical libraries that you would use with it. We will first cover what you need to know to build your own auto-configuration and we will move on to the typical steps required to create a custom starter.

Tip	A demo project is available to showcase how you can create a starter step by step.

Understanding auto-configured beans

Under the hood, auto-configuration is implemented with standard @Configuration classes. Additional @Conditional annotations are used to constrain when the auto-configuration should apply. Usually auto-configuration classes use @ConditionalOnClass and @ConditionalOnMissingBean annotations. This ensures that auto-configuration only applies when relevant classes are found and when you have not declared your own @Configuration.

You can browse the source code of {sc-spring-boot-autoconfigure}[spring-boot-autoconfigure] to see the @Configuration classes that we provide (see the {github-code}/spring-boot-autoconfigure/src/main/resources/META-INF/spring.factories[META-INF/spring.factories] file).

Locating auto-configuration candidates

Spring Boot checks for the presence of a META-INF/spring.factories file within your published jar. The file should list your configuration classes under the EnableAutoConfiguration key.

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.mycorp.libx.autoconfigure.LibXAutoConfiguration,\
com.mycorp.libx.autoconfigure.LibXWebAutoConfiguration

You can use the {sc-spring-boot-autoconfigure}/AutoConfigureAfter.{sc-ext}[@AutoConfigureAfter] or {sc-spring-boot-autoconfigure}/AutoConfigureBefore.{sc-ext}[@AutoConfigureBefore] annotations if your configuration needs to be applied in a specific order. For example, if you provide web-specific configuration, your class may need to be applied after WebMvcAutoConfiguration.

If you want to order certain auto-configurations that shouldn’t have any direct knowledge of each other, you can also use @AutoconfigureOrder. That annotation has the same semantic as the regular @Order annotation but provides a dedicated order for auto-configuration classes.

Note	Auto-configurations have to be loaded that way only. Make sure that they are defined in a specific package space and that they are never the target of component scan in particular.

Condition annotations

You almost always want to include one or more @Conditional annotations on your auto-configuration class. The @ConditionalOnMissingBean is one common example that is used to allow developers to ‘override’ auto-configuration if they are not happy with your defaults.

Spring Boot includes a number of @Conditional annotations that you can reuse in your own code by annotating @Configuration classes or individual @Bean methods.

Class conditions

The @ConditionalOnClass and @ConditionalOnMissingClass annotations allows configuration to be included based on the presence or absence of specific classes. Due to the fact that annotation metadata is parsed using ASM you can actually use the value attribute to refer to the real class, even though that class might not actually appear on the running application classpath. You can also use the name attribute if you prefer to specify the class name using a String value.

Tip	If you are using @ConditionalOnClass or @ConditionalOnMissingClass as a part of a meta-annotation to compose your own composed annotations you must use name as referring to the class in such a case is not handled.

Bean conditions

The @ConditionalOnBean and @ConditionalOnMissingBean annotations allow a bean to be included based on the presence or absence of specific beans. You can use the value attribute to specify beans by type, or name to specify beans by name. The search attribute allows you to limit the ApplicationContext hierarchy that should be considered when searching for beans.

Tip

You need to be very careful about the order that bean definitions are added as these conditions are evaluated based on what has been processed so far. For this reason, we recommend only using @ConditionalOnBean and @ConditionalOnMissingBean annotations on auto-configuration classes (since these are guaranteed to load after any user-define beans definitions have been added).

Note	@ConditionalOnBean and @ConditionalOnMissingBean do not prevent @Configuration classes from being created. Using these conditions at the class level is equivalent to marking each contained @Bean method with the annotation.

Property conditions

The @ConditionalOnProperty annotation allows configuration to be included based on a Spring Environment property. Use the prefix and name attributes to specify the property that should be checked. By default any property that exists and is not equal to false will be matched. You can also create more advanced checks using the havingValue and matchIfMissing attributes.

Resource conditions

The @ConditionalOnResource annotation allows configuration to be included only when a specific resource is present. Resources can be specified using the usual Spring conventions, for example, file:/home/user/test.dat.

Web application conditions

The @ConditionalOnWebApplication and @ConditionalOnNotWebApplication annotations allow configuration to be included depending on whether the application is a 'web application'. A web application is any application that is using a Spring WebApplicationContext, defines a session scope or has a StandardServletEnvironment.

SpEL expression conditions

The @ConditionalOnExpression annotation allows configuration to be included based on the result of a {spring-reference}/#expressions[SpEL expression].

Creating your own starter

A full Spring Boot starter for a library may contain the following components:

• The autoconfigure module that contains the auto-configuration code.

• The starter module that provides a dependency to the autoconfigure module as well as the library and any additional dependencies that are typically useful. In a nutshell, adding the starter should be enough to start using that library.

Tip	You may combine the auto-configuration code and the dependency management in a single module if you don’t need to separate those two concerns.

Naming

Please make sure to provide a proper namespace for your starter. Do not start your module names with spring-boot, even if you are using a different Maven groupId. We may offer an official support for the thing you’re auto-configuring in the future.

Here is a rule of thumb. Let’s assume that you are creating a starter for "acme", name the auto-configure module acme-spring-boot-autoconfigure and the starter acme-spring-boot-starter. If you only have one module combining the two, use acme-spring-boot-starter.

Besides, if your starter provides configuration keys, use a proper namespace for them. In particular, do not include your keys in the namespaces that Spring Boot uses (e.g. server, management, spring, etc). These are "ours" and we may improve/modify them in the future in such a way it could break your things.

Make sure to trigger meta-data generation so that IDE assistance is available for your keys as well. You may want to review the generated meta-data (META-INF/spring-configuration-metadata.json) to make sure your keys are properly documented.

Autoconfigure module

The autoconfigure module contains everything that is necessary to get started with the library. It may also contain configuration keys definition (@ConfigurationProperties) and any callback interface that can be used to further customize how the components are initialized.

Tip	You should mark the dependencies to the library as optional so that you can include the autoconfigure module in your projects more easily. If you do it that way, the library won’t be provided and Spring Boot will back off by default.

Starter module

The starter is an empty jar, really. Its only purpose is to provide the necessary dependencies to work with the library; see it as an opinionated view of what is required to get started.

Do not make assumptions about the project in which your starter is added. If the library you are auto-configuring typically requires other starters, mention them as well. Providing a proper set of default dependencies may be hard if the number of optional dependencies is high as you should avoid bringing unnecessary dependencies for a typical usage of the library.

What to read next

If you want to learn more about any of the classes discussed in this section you can check out the {dc-root}[Spring Boot API documentation] or you can browse the {github-code}[source code directly]. If you have specific questions, take a look at the how-to section.

If you are comfortable with Spring Boot’s core features, you can carry on and read about production-ready features.