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:

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
  }
}

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 {
    //....
  }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://xmlns.jcp.org/xml/ns/javaee"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd"
       bean-discovery-mode="all">
    
    <interceptors>
        <class>com.wordpress.abhirockzz.test.CDIBasedInerceptor</class>
    </interceptors>
</beans>

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 programmatic 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).