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Application servers and environments supported by Weld

Using Weld with WildFly

WildFly 8 and newer come with pre-configured Weld. There is no configuration needed to use Weld (or CDI for that matter). You may still want to fine-tune Weld with additional configuration settings.

GlassFish

Weld is also built into GlassFish from V3 onwards. Since GlassFish V3 is the Java EE reference implementation, it supports all features of CDI. What better way for GlassFish to support these features than to use Weld, the CDI reference implementation? Just package up your CDI application and deploy.

Servlet containers (such as Tomcat or Jetty)

While CDI does not require support for servlet environments, Weld can be used in a servlet container, such as Tomcat or Jetty.

Note
 There is a major limitation to using a servlet container; Weld doesn’t support deploying session beans, injection using @EJB or @PersistenceContext, or using transactional events in servlet containers. For enterprise features such as these, you should really be looking at a Java EE application server.

Weld can be used as a library in an web application that is deployed to a Servlet container. You should add the weld-servlet-core as a dependency to your project:

<dependency>
    <groupId>org.jboss.weld.servlet</groupId>
    <artifactId>weld-servlet-core</artifactId>
    <version>{weldVersion}</version>
</dependency>

All the necessary dependencies (CDI API, Weld core) will be fetched transitively.

Alternatively, there is a shaded version with all the dependencies in a single jar file which is available as:

<dependency>
    <groupId>org.jboss.weld.servlet</groupId>
    <artifactId>weld-servlet-shaded</artifactId>
    <version>{weldVersion}</version>
</dependency>

In general, weld-servlet uses ServletContainerInitializer mechanism to hook into the life cycle of Servlet 3.x compatible containers.

In special cases when your Servlet container does not support ServletContainerInitializer or you need more control over the ordering of listeners (e.g. move Weld’s listener) to the beginning of the list so that CDI context are active during invocation of other listeners) you can register Weld’s listener manually in the WEB-INF/web.xml file of the application:

<listener>
   <listener-class>org.jboss.weld.environment.servlet.Listener</listener-class>
</listener>
Note
 There is quite a special use-case where one more special component must be involved. If you want the session context to be active during HttpSessionListener.sessionDestroyed() invocation when the session times out or when all the sessions are destroyed because the deployment is being removed then org.jboss.weld.servlet.WeldTerminalListener must be specified as the last one in your web.xml. This listener activates the session context before other listeners are invoked (note that the listeners are notified in reverse order when a session is being destroyed).

Tomcat

Tomcat 7 and 8 are supported. Context activation/deactivation and dependency injection into Servlets and Filters works out of the box. Injection into Servlet listeners works on Tomcat 7.0.50 and newer.

Binding BeanManager to JNDI

What does not work out of the box is binding BeanManager to JNDI. Tomcat has a read-only JNDI, so Weld can’t automatically bind the BeanManager extension SPI. To bind the BeanManager into JNDI, you should populate META-INF/context.xml in the web root with the following contents:

<Context>
   <Resource name="BeanManager"
      auth="Container"
      type="javax.enterprise.inject.spi.BeanManager"
      factory="org.jboss.weld.resources.ManagerObjectFactory"/>
</Context>

and make it available to your deployment by adding this to the bottom of web.xml:

<resource-env-ref>
   <resource-env-ref-name>BeanManager</resource-env-ref-name>
   <resource-env-ref-type>
      javax.enterprise.inject.spi.BeanManager
   </resource-env-ref-type>
</resource-env-ref>

Tomcat only allows you to bind entries to java:comp/env, so the BeanManager will be available at java:comp/env/BeanManager

Embedded Tomcat

With embedded Tomcat it is necessary to register Weld’s listener programmatically:

public class Main {

    public static void main(String[] args) throws ServletException, LifecycleException {
        Tomcat tomcat = new Tomcat();
        Context ctx = tomcat.addContext("/", new File("src/main/resources").getAbsolutePath());

        Tomcat.addServlet(ctx, "hello", HelloWorldServlet.class.getName());
        ctx.addServletMapping("/*", "hello");

        // ctx.addApplicationListener(Listener.class.getName()); # (1)

        tomcat.start();
        tomcat.getServer().await();
    }

    public static class HelloWorldServlet extends HttpServlet {

        @Inject
        private BeanManager manager;

        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.setContentType("text/plain");
            resp.getWriter().append("Hello from " + manager);
        }
    }
}

  1. Weld’s org.jboss.weld.environment.servlet.Listener registered programmatically

Jetty

Jetty 7, 8 and 9 are supported. Context activation/deactivation and dependency injection into Servlets and Filters works out of the box. Injection into Servlet listeners works on Jetty 9.1.1 and newer.

Class Loading

No further configuration is needed when starting Jetty as an embedded webapp server from within another Java program. However, if you’re using a Jetty standalone instance one more configuration step is required.

The reason is that since Jetty 8 some internal classes are not visible from the web application. See also Setting Server Classes. Therefore, we have to tell Jetty not to hide the system classes which Weld integration code is using. Unfortunately, it’s not so simple. The only workaround is to use a Jetty Deployable Descriptor XML File (this is a Jetty 9 feature, in Jetty 8 a similar feature is incorporated - ContextProvider). For instance, if there is an application archive named weld-numberguess.war deployed in the webapps directory, an XML descriptor named weld-numberguess.xml should be created in the same directory (the file should have the same base name as the war - see alse the scanning rules described in Jetty docs):

<?xml version="1.0"?>
<!DOCTYPE Configure PUBLIC "-//Mort Bay Consulting//DTD Configure//EN" "http://www.eclipse.org/jetty/configure_9_0.dtd">
<Configure class="org.eclipse.jetty.webapp.WebAppContext">
  <Set name="contextPath">/weld-numberguess</Set>
  <Set name="war"><Property name="jetty.webapps" default="."/>/weld-numberguess.war</Set>
  <Call name="prependServerClass">
    <Arg>-org.eclipse.jetty.server.handler.ContextHandler</Arg>
  </Call>
  <Call name="prependServerClass">
    <Arg>-org.eclipse.jetty.servlet.FilterHolder</Arg>
  </Call>
  <Call name="prependServerClass">
    <Arg>-org.eclipse.jetty.servlet.ServletContextHandler</Arg>
  </Call>
  <Call name="prependServerClass">
    <Arg>-org.eclipse.jetty.servlet.ServletHolder</Arg>
  </Call>
</Configure>
Tip
 Jetty distributions (from version 9.2.4) contain a dedicated CDI/Weld module which allows to deploy a CDI application without bundling the Weld Servlet integration code.
Binding BeanManager to JNDI

To bind the BeanManager into JNDI, you should either populate WEB-INF/jetty-env.xml with the following contents:

<!DOCTYPE Configure PUBLIC "-//Mort Bay Consulting//DTD Configure//EN"
   "http://www.eclipse.org/jetty/configure.dtd">

<Configure id="webAppCtx" class="org.eclipse.jetty.webapp.WebAppContext">
    <New id="BeanManager" class="org.eclipse.jetty.plus.jndi.Resource">
        <Arg> <Ref id="webAppCtx"/> </Arg>
        <Arg>BeanManager</Arg>
        <Arg>
            <New class="javax.naming.Reference">
                <Arg>javax.enterprise.inject.spi.BeanManager</Arg>
                <Arg>org.jboss.weld.resources.ManagerObjectFactory</Arg>
                <Arg/>
            </New>
        </Arg>
    </New>
</Configure>

Or you can configure a special Servlet listener to bind the BeanManager automatically:

<listener>
   <listener-class>org.jboss.weld.environment.servlet.BeanManagerResourceBindingListener</listener-class>
</listener>

Just like in Tomcat, you need to make the BeanManager available to your deployment by adding this to the bottom of web.xml:

<resource-env-ref>
   <resource-env-ref-name>BeanManager</resource-env-ref-name>
   <resource-env-ref-type>
      javax.enterprise.inject.spi.BeanManager
   </resource-env-ref-type>
</resource-env-ref>

Jetty only allows you to bind entries to java:comp/env, so the BeanManager will be available at java:comp/env/BeanManager.

Embedded Jetty

When starting embedded Jetty programmatically from the main method it is necessary to register Weld’s listener:

public class Main {

    public static void main(String[] args) throws Exception {
        Server jetty = new Server(8080);
        WebAppContext context = new WebAppContext();
        context.setContextPath("/");
        context.setResourceBase("src/main/resources");
        jetty.setHandler(context);
        context.addServlet(HelloWorldServlet.class, "/*");

        context.addEventListener(new Listener()); # (1)

        jetty.start();
        jetty.join();
    }

    public static class HelloWorldServlet extends HttpServlet {

        @Inject BeanManager manager;

        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.setContentType("text/plain");
            resp.getWriter().append("Hello from " + manager);
        }
    }
}

  1. Weld’s org.jboss.weld.environment.servlet.Listener registered programmatically:

Undertow

Weld supports context activation/deactivation and dependency injection into Servlets when running on Undertow. Injection into Filters and Servlet listeners is not currently supported. Weld’s listener needs to be registered programmatically:

public class Main {

    public static void main(String[] args) throws ServletException {
        DeploymentInfo servletBuilder = Servlets.deployment()
                .setClassLoader(Main.class.getClassLoader())
                .setResourceManager(new ClassPathResourceManager(Main.class.getClassLoader()))
                .setContextPath("/")
                .setDeploymentName("test.war")
                .addServlet(Servlets.servlet("hello", HelloWorldServlet.class).addMapping("/*"))

                .addListener(Servlets.listener(Listener.class)); # (1)

        DeploymentManager manager = Servlets.defaultContainer().addDeployment(servletBuilder);
        manager.deploy();

        HttpHandler servletHandler = manager.start();
        PathHandler path = Handlers.path(Handlers.redirect("/")).addPrefixPath("/", servletHandler);
        Undertow server = Undertow.builder().addHttpListener(8080, "localhost").setHandler(path).build();
        server.start();
    }

    public static class HelloWorldServlet extends HttpServlet {

        @Inject BeanManager manager;

        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.setContentType("text/plain");
            resp.getWriter().append("Hello from " + manager);
        }
    }
}

  1. Weld’s org.jboss.weld.environment.servlet.Listener registered programmatically:

WildFly Web

WildFly Web is a lightweight Servlet container that uses Undertow. Weld supports context activation/deactivation and dependency injection into Servlets. Injection into Filters and Servlet listeners is not currently supported. Weld integration is started automatically when weld-servlet is part of your application.

Bean Archive Isolation

By default, bean archive isolation is enabled. It means that alternatives, interceptors and decorators can be selected/enabled for a bean archive by using a beans.xml descriptor.

This behaviour can be changed by setting the servlet initialization parameter org.jboss.weld.environment.servlet.archive.isolation to false. In this case, Weld will use a "flat" deployment structure - all bean classes share the same bean archive and all beans.xml descriptors are automatically merged into one. Thus alternatives, interceptors and decorators selected/enabled for a bean archive will be enabled for the whole application.

Note
 Bean archive isolation is supported (and enabled by default) from version 2.2.5.Final. Previous versions only operated with the "flat" deployment structure.

Implicit Bean Archive Support

CDI 1.1 introduced the bean discovery mode of annotated used for implicit bean archives (see also [packaging-and-deployment]). This mode may bring additional overhead during container bootstrap. Therefore, Weld Servlet supports the use of Jandex bytecode scanning library to speed up the scanning process. Simply put the jandex.jar on the classpath. If Jandex is not found on the classpath Weld will use the Java Reflection as a fallback.

In general, an implicit bean archive does not have to contain a beans.xml descriptor. However, such a bean archive is not supported by Weld Servlet, i.e. it’s excluded from discovery.

Note
 The bean discovery mode of annotated is supported from version 2.2.5.Final. Previous versions processed implicit bean archives in the same way as explicit bean archives.

Java SE

In addition to improved integration of the Enterprise Java stack, the "Contexts and Dependency Injection for the Java EE platform" specification also defines a state of the art typesafe, stateful dependency injection framework, which can prove useful in a wide range of application types. To help developers take advantage of this, Weld provides a simple means for being executed in the Java Standard Edition (SE) environment independently of any Java EE APIs.

When executing in the SE environment the following features of Weld are available:

  • Managed beans with @PostConstruct and @PreDestroy lifecycle callbacks

  • Dependency injection with qualifiers and alternatives

  • @Application, @Dependent and @Singleton scopes

  • Interceptors and decorators

  • Stereotypes

  • Events

  • Portable extension support

EJB beans are not supported.

CDI SE Module

Weld provides an extension which will boot a CDI bean manager in Java SE, automatically registering all simple beans found on the classpath. The command line parameters can be injected using either of the following:

@Inject @Parameters List<String> params;
@Inject @Parameters String[] paramsArray;

The second form is useful for compatibility with existing classes.

Note
 The command line parameters do not become available for injection until the ContainerInitialized event is fired. If you need access to the parameters during initialization you can do so via the public static String[] getParameters() method in StartMain.

Here’s an example of a simple CDI SE application:

import javax.inject.Singleton;

@Singleton
public class HelloWorld
{
   public void printHello(@Observes ContainerInitialized event, @Parameters List<String> parameters) {
       System.out.println("Hello " + parameters.get(0));
   }
}
Note
 Weld automatically registers shutdown hook during initialization in order to properly terminate all running containers should the VM be terminated or program exited. Even though it is possible to register an alternative hook and implement the logic, it is not recommended. The behavior across OS platforms may differ and specifically on Windows it proves to be problematic.

Bootstrapping CDI SE

CDI SE applications can be bootstrapped in the following ways.

The ContainerInitialized Event

Thanks to the power of CDI’s typesafe event model, application developers need not write any bootstrapping code. The Weld SE module comes with a built-in main method which will bootstrap CDI for you and then fire a ContainerInitialized event. The entry point for your application code would therefore be a simple bean which observes the ContainerInitialized event, as in the previous example.

In this case your application can be started by calling the provided main method like so:

java org.jboss.weld.environment.se.StartMain <args>
Programmatic Bootstrap API

For added flexibility, CDI SE also comes with a bootstrap API which can be called from within your application in order to initialize CDI and obtain references to your application’s beans and events. The API consists of two classes: Weld and WeldContainer.

/** A builder used to bootsrap a Weld SE container. */
public class Weld
{

   /** Boots Weld and creates and returns a WeldContainer instance, through which
    * beans and events can be accesed. */
   public WeldContainer initialize() {...}

   /** Convenience method for shutting down all the containers initialized by a specific builder instance. */
   public void shutdown() {...}

}
/** Represents a Weld SE container. */
public class WeldContainer implements javax.enterprise.inject.Instance<Object>
{

   /** Provides access to all events within the application. */
   public Event<Object> event() {...}

   /** Provides direct access to the BeanManager. */
   public BeanManager getBeanManager() {...}

   /** Returns the identifier of the container */
   String getId() {...}

   /** Shuts down the container. */
   public void shutdown() {...}

   /** Returns the running container with the specified identifier or null if no such container exists */
   public static WeldContainer instance(String id) {...}

}

Here’s an example application main method which uses this API to bootsrap a Wedl SE container and call a business method of a bean MyApplicationBean.

import org.jboss.weld.environment.se.Weld;

public static void main(String[] args) {
   Weld weld = new Weld();
   WeldContainer container = weld.initialize();
   container.select(MyApplicationBean.class).get().callBusinessMethod();
   container.shutdown();
}

Alternatively the application could be started by firing a custom event which would then be observed by another simple bean. The following example fires MyEvent on startup.

org.jboss.weld.environment.se.Weld;

public static void main(String[] args) {
   Weld weld = new Weld();
   WeldContainer container = weld.initialize();
   container.event().select(MyEvent.class).fire( new MyEvent() );
   // When all observer methods are notified the container shuts down
   container.shutdown();
}

Because WeldContainer implements AutoCloseable, it can be used within a try-with-resources block. Should the execution get out of the code block, the Weld instance is shut down and all managed instances are safely destroyed. Here is an example using the above code but leaving out the shutdown() method:

org.jboss.weld.environment.se.Weld;

public static void main(String[] args) {
   Weld weld = new Weld();
   try (WeldContainer container = weld.initialize()) {
      container.select(MyApplicationBean.class).get().callBusinessMethod();
   }
}

In case of more complex scenarios, it might be handy to gain higher level of control over the bootstraping process. Using the builder, it is possible to disable automatic scanning and to explicitly select classes/packages which will be managed by Weld. Interceptors, decorators and extensions can be defined in the very same manner. Last but not least, builder can be used to set Weld-specific configuration. Following example demonstrates these features:

Weld weld = new Weld()
    .disableDiscovery()
    .packages(Main.class, Utils.class)
    .interceptors(TransactionalInterceptor.class)
    .property("org.jboss.weld.construction.relaxed", true);

try (WeldContainer container = weld.initialize()) {
    MyBean bean = container.select(MyBean.class).get();
    System.out.println(bean.computeResult());
}

Furthermore, it is also possible to create several independent Weld instances. Code snippet below shows how achieve that:

Weld weld = new Weld()
    .disableDiscovery();

weld.containerId("one").beanClasses(MyBean.class).initialize();
weld.containerId("two").beanClasses(OtherBean.class).initialize();

MyBean bean = WeldContainer.instance("one").select(MyBean.class).get();
System.out.println(bean.computeResult());

// Shutdown the first container
WeldContainer.instance("one").shutdown();

// Shutdown all the containers initialized by the builder instance
weld.shutdown();

Thread Context

In contrast to Java EE applications, Java SE applications place no restrictions on developers regarding the creation and usage of threads. Therefore Weld SE provides a custom scope annotation, @ThreadScoped, and corresponding context implementation which can be used to bind bean instances to the current thread. It is intended to be used in scenarios where you might otherwise use ThreadLocal, and does in fact use ThreadLocal under the hood.

To use the @ThreadScoped annotation you need to enable the RunnableDecorator which 'listens' for all executions of Runnable.run() and decorates them by setting up the thread context beforehand, bound to the current thread, and destroying the context afterwards.

<beans>
  <decorators>
     <class>org.jboss.weld.environment.se.threading.RunnableDecorator</class>
  </decorator>
</beans>
Note
 It is not necessary to use @ThreadScoped in all multithreaded applications. The thread context is not intended as a replacement for defining your own application-specific contexts. It is generally only useful in situations where you would otherwise have used ThreadLocal directly, which are typically rare.

Setting the Classpath

Weld SE comes packaged as a 'shaded' jar which includes the CDI API, Weld Core and all dependent classes bundled into a single jar. Therefore the only Weld jar you need on the classpath, in addition to your application’s classes and dependent jars, is the Weld SE jar. If you are working with a pure Java SE application you launch using java, this may be simpler for you.

If you prefer to work with individual dependencies, then you can use the weld-se-core jar which just contains the Weld SE classes. Of course in this mode you will need to assemble the classpath yourself.

If you work with a dependency management solution such as Maven you can declare a dependency such as:

<dependency>
   <groupId>org.jboss.weld.se</groupId>
   <artifactId>weld-se-shaded</artifactId>
</dependency>

Bean Archive Isolation

By default, bean archive isolation is enabled. It means that alternatives, interceptors and decorators can be selected/enabled for a bean archive by using a beans.xml descriptor.

This behaviour can be changed by providing a system property org.jboss.weld.se.archive.isolation with value of false. In this case, Weld will use a "flat" deployment structure - all bean classes share the same bean archive and all beans.xml descriptors are automatically merged into one. Thus alternatives, interceptors and decorators selected/enabled for a bean archive will be enabled for the whole application.

Note
 Bean archive isolation is supported (and enabled by default) from version 2.2.0.Final. Previous versions only operated with the "flat" deployment structure.

Implicit Bean Archive Support

CDI 1.1 introduced the bean discovery mode of annotated used for implicit bean archives (see also [packaging-and-deployment]). This mode may bring additional overhead during container bootstrap. Therefore, Weld Servlet supports the use of Jandex bytecode scanning library to speed up the scanning process. Simply put the jandex.jar on the classpath. If Jandex is not found on the classpath Weld will use the Java Reflection as a fallback.

In general, an implicit bean archive does not have to contain a beans.xml descriptor. However, such a bean archive is not supported by Weld SE, i.e. it’s excluded from discovery.

Note
 The bean discovery mode of annotated is supported from version 2.2.0.Final. Previous versions processed implicit bean archives in the same way as explicit bean archives.

OSGi

Weld supports OSGi environment through Pax CDI. For more information on using Weld in OSGi environment check Pax CDI documentation . In addition, Weld comes with a sample application called Paint which demonstrates how to use CDI with OSGi. Check examples/osgi/README.md for more information.