WebSocket and CDI integration.. again..

In one of my older blog posts, I had written about what does not work as far as WebSocket and CDI integration within the Java EE Platform 😉 This one talks about what’s possible with CDI in terms of

• Dependency Injection
• Interceptors

Before you dig in, here is a summary

Feature	Supported in EJB Annotated WebSocket endpoint ?	Supported in Plain WebSocket endpoint ?
Inject CDI managed beans	yes	yes
Use CDI interceptors	yes	yes

DI support

It is possible to inject CDI managed beans in WebSocket endpoints. All injection targets are supported i.e. field, constructor, method

	@RequestScoped //CDI annotation
	public class CDIManagedBean {
	….
	}
	@ServerEndpoint("/stocks/")
	public class StockTracker {
	@Inject
	private CDIManagedBean cdiBean;
	@OnOpen
	public void onOpenCallback(Session s){
	cdiBean.doSomething(); //use injected instance
	}
	}
	// works with an EJB as well
	@ServerEndpoint("/weather/")
	@Stateless
	public class WeatherTracker {
	@Inject
	private CDIManagedBean cdiBean;
	@OnOpen
	public void onOpenCallback(Session s){
	cdiBean.doSomething(); //use injected instance
	}
	}

view raw

WebSocket-CDI-snippets.txt

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Interceptor support

You can use interceptors to implement cross-cutting concerns in for the business methods in your WebSocket endpoints

	//the interceptor binding
	@Inherited
	@InterceptorBinding
	@Retention(RUNTIME)
	@Target({METHOD, TYPE})
	public @interface LoggerInterceptorBinding {}
	//Implement our interceptor and bind it
	@Interceptor
	@LoggerInterceptorBinding
	public class CDIBasedLoggingInterceptor {
	@AroundInvoke
	public Object log(InvocationContext ic) throws Exception {
	Object retVal = null;
	String clazz = ic.getTarget().getClass().getName();
	try {
	Logger.enter(clazz);
	retVal = ic.proceed();
	} catch (Exception e) {
	throw e;
	} finally {
	Logger.exit(clazz);
	}
	return retVal;
	}
	}
	//Apply the interceptor where needed (via the binding)
	@ServerEndpoint("/chat/")
	public class ChatEndpoint {
	@LoggerInterceptorBinding //binding the CDIBasedLoggingInterceptor
	@OnOpen
	public void onChatMsgRecieved {
	//….
	}
	}
	//don't forget to specify the interceptor in beans.xml (compulsory)\
	<?xml version="1.0" encoding="UTF-8"?>
	<beans xmlns="http://xmlns.jcp.org/xml/ns/javaee&quot;
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance&quot;
	xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd&quot;
	bean-discovery-mode="all">
	<interceptors>
	<class>com.wordpress.abhirockzz.test.CDIBasedInerceptor</class>
	</interceptors>
	</beans>

view raw

WebSocket-Interceptors-snippet.txt

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Good to know

Now that you have an idea about how WebSockets work with CDI in terms of Dependency injection and Interceptors, here are some other points

• DI and interceptors are supported for both server and client endpoints running within a JavaEE container
• DI and interceptors are supported for both annotated and programatic endpoints running within a JavaEE container
• container managed injection features are not available to WebSocket endpoints which override the container implemented initialization (using the ServerEndpointConfig.Configurator)

Additional reading

• eBook – Java WebSocket API Handbook
• WebSocket specification
• Previous blogs related to WebSocket
• CDI specification

 

Cheers!