Quick tip: managing Stateful EJBs in WebSocket endpoints

@Stateful EJBs can be injected in WebSocket endpoints (supported by the WebSocket specification). There is an one-to-one association between the WebSocket client & endpoint (which is by default) as well as the injected Stateful EJB instance, which makes it an good candidate for storing client specific state. It offers advanced semantics as compared to simple java.util.Map interface exposed by getUserProperties method in javax.websocket.Session)

	@Stateful
	public class ClientChatState {
	//…who needs details !
	}
	@ServerEndpoint("/letschat/{login-id}")
	public class ChatEndpoint {
	@EJB
	private ClientChatState ccs; //stateful EJB
	private String userID;
	@OnOpen
	public void connOpened(@PathParam("login-id") String loginID, Session session) {
	ccs.setUser(loginID)
	.currentState(State.JOINED); //everyone likes a fluent API!
	}
	….
	}

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StatefulEJBInWebSocket_1.txt

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But, what happens to the EJB when ….

… the WebSocket session terminates (either from the client or server side) ?? The Stateful instance can still linger in memory before its destroyed

• Their removal can be tuned by using the @StatefulTimeout annotation (but why wait ??), or
• you can choose to passivate them by using passivationCapable=true with  @Stateful (but why passivate the EJB when the WebSocket connection itself is closed ?)

The Tip

Implement a @Remove annotated method in the Stateful EJB and call it from the @OnClose callback method ni your WebSocket server endpoint implementation. This will ensure that the  EJB is removed from the memory immediately rather than depending upon other factors

	@Stateful
	public class ClientChatState {
	…
	@Remove
	public void dispose(){
	//this can just be a marker method
	}
	@PreDestroy
	public void closeResources(){
	//close connections, resources etc.
	}
	}
	@ServerEndpoint("/letschat/{login-id}")
	public class ChatEndpoint {
	….
	@OnClose
	public void disconnected(Session session) {
	ccs.dispose(); //method annotated with @Remove
	}
	….
	}

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StatefulEJBInWebSocket_2.txt

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Further reading

• eBook: Java WebSocket API Handbook
• JSR 356 specification
• eBook: EJB Annotations Primer
• Tyrus (JSR 356 RI)

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