How to wait for Spring WebSocketStompClient to connect

Question

I am using this guide to implement a simple Stomp client:

WebSocketClient webSocketClient = new StandardWebSocketClient();
WebSocketStompClient stompClient = new WebSocketStompClient(webSocketClient);

ThreadPoolTaskScheduler taskScheduler = new ThreadPoolTaskScheduler();
taskScheduler.afterPropertiesSet();
stompClient.setTaskScheduler(taskScheduler); // for heartbeats

stompClient.setMessageConverter(new StringMessageConverter());

StompSessionHandler sessionHandler = new MySessionHandler();
stompClient.connect("ws://server/endpoint", sessionHandler);

// WAITING HERE

When connection completes it's supposed to report to MySessionHandler asynchronously:

public class MySessionHandler extends StompSessionHandlerAdapter
{
     @Override
     public void afterConnected(StompSession session, StompHeaders connectedHeaders) 
     {
         // WAITING FOR THIS
     }
}

So question is: how the line WAITING HERE should wait for the line WAITING FOR THIS? Is there a specific Spring way of doing this? If not, which generic Java way fits here the best?

vsminkov · Accepted Answer · 2016-08-23T22:43:38.647

Maybe a java.util.concurrent.CountDownLatch may solve your problem like this:

CountDownLatch latch = new CountDownLatch(1);
StompSessionHandler sessionHandler = new MySessionHandler(latch);
stompClient.connect("ws://server/endpoint", sessionHandler);
// wait here till latch will be zero
latch.await();

And your MySessionHandler implementation:

public class MySessionHandler extends StompSessionHandlerAdapter {
    private final CountDownLatch latch;

    public MySessionHandler(final CountDownLatch latch) {
        this.latch = latch;
    }

    @Override
    public void afterConnected(StompSession session, 
                               StompHeaders connectedHeaders) {
        try {
            // do here some job
        } finally {
            latch.countDown();
        }
    }
}

timbre timbre · Answer 2 · 2017-12-20T20:32:56.047

7

The solution with latch works. Later I discovered that connect function returns ListenableFuture<StompSession>, so we can wait for session to be created like this:

ListenableFuture<StompSession> future = 
                 stompClient.connect("ws://server/endpoint", sessionHandler);
StompSession session = future.get(); // <--- this line will wait just like afterConnected()

edited Dec 20 '17 at 20:32

answered Aug 23 '16 at 22:48

timbre timbre

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future.get() will give you the session object, which you were supposed to get from afterConnect.. – rxx Sep 30 '17 at 23:30

score 1 · Answer 3 · answered Nov 07 '16 at 21:33

You don need latch, nothing, afterConnected method will be executed only when connection is stablished.

My example:

URI stompUrlEndpoint = new URI("localhost:8080/Serv/enpoint");

ThreadPoolTaskScheduler taskScheduler = new ThreadPoolTaskScheduler();
//Calls initialize() after the container applied all property values.
taskScheduler.afterPropertiesSet();

StandardWebSocketClient webSocketClient = new StandardWebSocketClient();
List<Transport> transports = new ArrayList<>(2);

transports.add(new WebSocketTransport(webSocketClient));

SockJsClient sockJsClient = new SockJsClient(transports);   

WebSocketStompClient stompClient = new WebSocketStompClient(sockJsClient);

stompClient.setMessageConverter(new SimpleMessageConverter());          // default converter: SimpleMessageConverter

// Configure a scheduler to use for heartbeats and for receipt tracking. 
stompClient.setTaskScheduler(taskScheduler);

StompSessionHandlerImp stompSessionHandlerImp = new StompSessionHandlerImp();

ListenableFuture<StompSession> stompSessionFuture2 = stompClient.connect(stompUrlEndpoint.toString(), stompSessionHandlerImp);


try {
            stompSession = stompSessionFuture.get(10, TimeUnit.SECONDS);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ExecutionException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (TimeoutException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }


       private class StompSessionHandlerImp extends StompSessionHandlerAdapter {
           private StompSession session;


          @Override
          public void afterConnected(StompSession session, StompHeaders connectedHeaders) {
          this.session =  session;

          session.setAutoReceipt(true);
          session.subscribe("/user/queue/bancaria.readcard", new StompFrameHandler() {
            ...
       }
 }

}

How to wait for Spring WebSocketStompClient to connect

3 Answers3