java - Integrating JSR-356 WebSocket @ServerEndpoint with Spring 3 beans

Question

I'm using Spring 3.2.5 without full new JSR-356 WebSockets support.

I would like to have singleton-bean reference in my @ServerEndpoint WebSocket server, which is instantiated by servlet container itself, not in Spring context.

What is the clean way to do it?

My current solution: I made @Service singleton bean with instance in static field:

@Service
public class WebSocketSupportBean {
    private volatile static WebSocketSupportBean instance = null;

    public static WebSocketSupportBean getInstance() {
        return instance;
    }

    public WebSocketSupportBean() {
        instance = this;
    }

and just getting it in @ServerEndpoint by static method, disconnecting user if null returned (if bean not jet created during server startup but user connects):

Answer 1

You can setup websockets with spring framework 3.x

I developed a small proof-of-concept application to demonstrate how, based on Rossen Stoyanchev's SpringConfiguration released with spring-core 4.0.

The application sets up a websocket server endpoint with uri /wstest which will use a @Autowired spring bean to select a greeting word and reply to a websocket message.

The websocket connection is initiated and messages sent by an html page (index.html) running in a browser that supports websockets.

The Endpoint registration is made by a ServletContextListener at context initialization and when the endpoint is instantiated it will be wired with spring:

@WebListener
public class MyApplication implements ServletContextListener {

    private final static String SERVER_CONTAINER_ATTRIBUTE = "javax.websocket.server.ServerContainer";

    @Override
    public void contextInitialized(ServletContextEvent sce) {

        ServletContext container = sce.getServletContext();

        final ServerContainer serverContainer = (ServerContainer) container.getAttribute(SERVER_CONTAINER_ATTRIBUTE);
        try {
            serverContainer.addEndpoint(new MyEndpointConfig(MyEndpoint.class, "/wstest"));
        } catch (DeploymentException e) {
            e.printStackTrace();
        }
    }
}

And the Endpoint is:

@Component
public class MyEndpoint extends Endpoint {

    @Autowired
    MyService myService;

    @Override
    public void onOpen(Session session, EndpointConfig config) {

        session.addMessageHandler(new MyMessageHandler(session));
    }


    class MyMessageHandler implements MessageHandler.Whole<String> {

        final Session session;

        public MyMessageHandler(Session session) {
            this.session = session;
        }

        @Override
        public void onMessage(String message) {
            try {
                String greeting = myService.getGreeting();
                session.getBasicRemote().sendText(greeting + ", got your message (" + message + "). Thanks ! (session: " + session.getId() + ")");
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Checkout the full source and ready to run example on my Github page.