如何等待 Spring WebSocketStompClient 连接

Question

我正在使用本指南来实现一个简单的 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

当连接完成时，它应该MySessionHandler异步报告：

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

所以问题是：线路WAITING HERE应该如何等待线路WAITING FOR THIS？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？

Answer 1

也许 ajava.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();

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();
        }
    }
}

Answer 2

带闩锁的解决方案有效。后来我发现connect函数返回ListenableFuture<StompSession>，所以我们可以像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()