如何等待 Spring WebSocketStompClient 连接答案

【问题标题】：How to wait for Spring WebSocketStompClient to connect如何等待 Spring WebSocketStompClient 连接
【发布时间】：2016-08-14 22:02:42
【问题描述】：

我正在使用this guide 来实现一个简单的 Stomp 客户端：

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

连接完成后应该异步报告给MySessionHandler：

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

所以问题是：WAITING HERE 行应该如何等待WAITING FOR THIS 行？是否有特定的 Spring 方式来执行此操作？如果不是，哪种通用 Java 方式最适合这里？

【问题讨论】：

标签： java spring multithreading concurrency spring-websocket

【解决方案1】：

也许java.util.concurrent.CountDownLatch 可以像这样解决您的问题：

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();

还有你的MySessionHandler 实现：

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();
        }
    }
}

【讨论】：

【解决方案2】：

带有闩锁的解决方案有效。后来我发现connect函数返回ListenableFuture<StompSession>，所以我们可以这样等待会话被创建：

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

【讨论】：

future.get() 会给你会话对象，你应该从 afterConnect..

【解决方案3】：

你不需要latch，什么都不需要，afterConnected方法只有在连接建立后才会执行。

我的例子：

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() {
            ...
       }
 }

}

【讨论】：