Spring Framework/Boot Sample

This is a sample tutorial of Spring Framework 4.x (based on Spring Boot). Since samples from Spring official site are independent which is hard to have a big landscape from top, so:

• I create this single one project to integrate them all
• Also, as a practice of coding. (Talk is cheap, show me the code...)

Basically, it is an back-end side project, following topics will be covered:

• Spring Boot
• Spring MVC
• Spring Data
• Spring REST
• Spring Security
• Spring Test - TBC

Spring Boot - Setup

You need following tools to start:

• STS: Spring Tool Suit
• Maven 3.x (dependency and build)
• Postman
• Spring Guide and Samples

Then, you need to create a boot project from STS.

• File > New > Spring Starter Project ...

• Maven config

• Boot config, such as: boot version, dependencies (JPA, Security, REST...)

    // Spring Boot will generate a startup class for you automatically
    @SpringBootApplication
    public class WebappApplication {
    
    	public static void main(String[] args) {
    		SpringApplication.run(WebappApplication.class, args);
    	}
    }
  

Note: You can configure your pom.xml to adjust your dependencies accordingly later.

Project Structure

+ Project Name

	[BACK-END]
	- src/main/java
		- com.jasonshi.sample
			- config
			- controller
			- dto
			- init
			- entity
			- repository
			- security
			- service					
			
			
	- src/main/resources
		- template
	- src/test/java
	
	
	[FRONT-END]
	- src/main
		- webapp
			- resources
				- css
				- img
				- js
				- .html
		- test
		
	[OTHER]
	- pom.xml
	- README.md

---

Spring Security

	@Configurable
	@EnableWebSecurity
	public class WebappSecurity extends WebSecurityConfigurerAdapter{
		
		protected void configure(HttpSecurity http) throws Exception {
			// filter and permit url
		}
		
		@Autowired
		public void configure(AuthenticationManagerBuilder auth) throws Exception {
			// auth in memory or database ...
		}						
	} 

Spring Security - Customized UserDetailsService

In memory user/password/role is not suitable for production environment. We need to get them from database or somewhere else. So you could define your own authentication service:

 public class CustomizedUserDetailsService implements UserDetailsService {

	@Override
	public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
		// Use Service -> Repository (JPA/JDBC) to get data and encapsulate as UserDetails 
	}
}

Set this UserDetailsService into Security configuration.

@Autowired
private UserDetailsService userDetailsService;

@Autowired
public void configure(AuthenticationManagerBuilder auth) throws Exception {
	auth.userDetailsService(userDetailsService);
}		

Spring REST

Provide REST API and return json as response

http://localhost:8080/greeting?name=Jason


{
	"id":2,
	"content":"Hello, Jason!"
}

How?

• Define Model

  public class Greeting{...}

• Define Controller

  @RestController public class GreetingController { private static final String template = "Hello, %s!"; private AtomicLong counter = new AtomicLong(); @RequestMapping("/greeting") public Greeting greeting(@RequestParam(value = "name", defaultValue = "King of the world") String name) { return new Greeting(counter.incrementAndGet(), String.format(template, name)); } }

• Configure to scan controllers from package

  @Configuration @EnableWebMvc @ComponentScan("com.jasonshi.sample.controller") public class WebappMVC extends WebMvcConfigurerAdapter {...}

Spring DATA - Repository REST

Provide REST API for Device entity from Table Level (h2 memory table)

	http://localhost:8080/device

POM:

	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-data-jpa</artifactId>
	</dependency>
	
	<dependency>
		<groupId>com.h2database</groupId>
		<artifactId>h2</artifactId>
	</dependency>
	
	<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-rest</artifactId>
   </dependency>

How?

• Define Entity

    @Entity
    public class Device {...}
  

• Define REST Repository (DAO)

    @RepositoryRestResource(collctionResourceRel = "device", path = "device")
    public interface DeviceRepository extends PagingAndSortingRepository<Device, Long> {
    
    	List<Device> findByName(@Param("name") String name);
    
    }
  

• Disable CSRF for Basic authentication (or cannot get/post using Postman/Curl)

    @Override
    protected void configure(HttpSecurity http) throws Exception {
    	http
    	.csrf().disable();
    	...
    }
  

• Use POSTMAN or cURL to manipulate ... (Add a device)

    POST /device HTTP/1.1
    Host: localhost:8080
    Content-Type: application/json
    Cache-Control: no-cache
    Postman-Token: 47baf1c3-4785-5ba9-ac4b-a3714ff43fcf
    
    {
        "name":"device1",
        "desc":"this is device 1"
    }
  

**NOTE: **This REST API is not secured. We will secure it with Basic Authentication Later.

Spring REST Security

Spring JPA

Still a lot to learn the specification of JPA. TBC...

• @Entity, @OneToMany, @ManyToMany, @JoinTable @JoinTable
• CrudRepository and its sub-classes

Spring MVC

Repository

Entity is a Java Object mapping to table of database. Repository is an entity manipulator which should be pure and should not contain business logic.

/** @Repository will only be needed here, but if you want to provide REST API for this repo, you can use @RepositoryRestResource */
@RepositoryRestResource(collectionResourceRel = "device", path = "device")
public interface DeviceRepository extends PagingAndSortingRepository<Device, Long> {
	List<Device> findByName(@Param("name") String name);
}

Service

Service is a reply on Repository and provide business extra logic, such as: check, exception, extra transition ...

@Service
public class DeviceService {
	
	@Autowired
	private DeviceRepository deviceRepo;
	
	@Transactional(readOnly = true)
	public List<Device> findDevice(String name) {}
}

Controller

Controller is a binder of Model and View

• Receive HTTPRequest

• Process... (invoke Services)

• Send back HTTPResponse

  @Controller @RequestMapping("dvc") // besides \device, this is another REST API public class DeviceController { @Autowired private DeviceService deviceService;

    @ResponseBody
    @ResponseStatus(HttpStatus.OK)
    @RequestMapping(method = RequestMethod.DELETE)
    public void deleteDevice(@RequestParam(value = "deviceId", defaultValue = "1") Long deviceId) {
    	deviceService.deleteDevice(deviceId);
    }
  

  }

  Method: DELETE http://localhost:8080/devices?id=1

Spring TEST

Spring is born for unit test. Why is that:

• Unit test's essential job is to: test its own logic.
• And eliminate the influence of other references. (use mock)

That's what Spring do: Using DI and AOP to loose coupling. All references are @Autowired

• We just need to (define and) use the interface
• Then use mockito to mock whatever(implementation of interface) we want

Other projects

Lombok

Lombok is project to simplify your POJO class.

• Need to install for IDE (such as Eclipse or STS)

• Import to project

  @Data @NoArgsConstructor public class Device { private long id; private String name; private String desc; }

Tutorial

Java Object Streaming over HTTP

• By default, the controller is asynchronized: Need to check whether it has problem or not

• ObjectInputStream, ObjectOutStream:

    Client Side: get from URL connection
  
    Server side: get from HttpServletRequest and HttpServletResponse
  

BEST PRACTICE

Security - Support both FormLogin & Basic Auth

Stackoverflow Answer

• Beware of the annotation, should be the same!

How many Servlet instances are created, based on multiple clients requst?

• Servlet instance will be singleton by default, but per request, there will be per thread to handle (in parallel)

    @Scope("singleton")	
  

• Meanwhile, you can change Servlet to multiple instances according to request, use following annotation

    @Scope("prototype") 
  

Servlet instances per requests

BOOKS

• Spring in Action (4th Edition)

TODO LIST

• Basic Authentication config: support multiple rest api

• Multiple data sources

• Spring Test

• Project init some data

• DetailsService: Sill need to write (Service), Repository(DAO) to get user/role from database.

• HttpSecurity interceptor syntax

• Need to think about @RequestParam, @RequestBody and REST handling in Controller!

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