Java Websocket/MessageHandler 返回全局范围？

Question

我面临以下问题，但尚未找到有效的解决方案。我有 3 个不同的应用程序，它们应该相互通信:

• 用户界面部分(1)
• 后端应用程序(2)
• “云端”微服务(3)

后端应用程序为 UI 提供 Web 服务 (REST)，以从微服务获取信息或将信息放入微服务。我想从微服务中获取的所有内容都工作正常，但是:如果我想将数据放入微服务，规范需要 websocket 连接。这也可以正常工作，但是微服务在(不)成功的命令之后返回一条消息，例如

{"statusCode":200,"messageId":"1234567890"}

现在的问题是:如何在应用程序中获取此消息并将其发送回 UI，以便用户知道命令是否成功？

目前我尝试过这个:

WebSocketClient.java

@OnMessage
public void onMessage(Session session, String msg) {
    if (this.messageHandler != null) {
        this.messageHandler.handleMessage(msg);
    }
}
public void addMessageHandler(MessageHandler msgHandler) {
    this.messageHandler = msgHandler;
}
public static interface MessageHandler {

    public String handleMessage(String message);
}

MyTotalAwesomeController.java

public class MyTotalAwesomeController {

    WebSocketClient wsc = new WebSocketClient();
    ...


    @RequestMapping(value="/add", method={RequestMethod.POST, RequestMethod.OPTIONS})
    public ResponseEntity<Object> putDataToMicroservice(@RequestBody Map<String, Object> payload, @RequestHeader(value = "authorization") String authorizationHeader) throws Exception {
    ...

    wsc.addMessageHandler(new WebSocketClient.MessageHandler() {
        public String handleMessage(String message) {

            System.out.println("RETURN MSG FROM WSS : " + message);
            return message;
        }
    });

    return ResponseEntity.ok("worked");
}

我可以看到 MessageHandler 返回的控制台输出，但我不知道如何将其传递给父方法以进行返回，而不是仅返回 ResponseEntity.ok()。

我还不太习惯 Java 中的 WebSocket 连接，所以请不要评判我;-)

感谢您的帮助。

Answer 1

下面的代码将在以下假设下工作:@OnMessage 方法在 WebSocket 客户端运行时管理的线程中执行。请检查运行 @OnMessage 方法的线程。

如果上述前提成立，则由全局范围内的线程执行的 putDataToMicroservice() 方法将等待，直到 WebSocket 响应到达 WS 客户端线程，该线程将重新传递消息到全局范围线程。然后 Controller 类中的执行将继续。

public class MyTotalAwesomeController {

    WebSocketClient wsc = new WebSocketClient();

    // Queue for communication between threads.
    private BlockingQueue<String> queue;

    @PostConstruct
    void init() {

        queue = new SynchronousQueue<>(true);

        // This callback will be invoked by the WebSocket thread.
        wsc.addMessageHandler(new WebSocketClient.MessageHandler() {
            @Override
            public String handleMessage(String message) {
                System.out.println("RETURN MSG FROM WSS : " + message);
                // Pass message to the controller thread.
                queue.put(message);
                // Note that the return value is not necessary.
                // You can take it out of the interface as well.
                return null;
            }
        });
    }

    @RequestMapping(value="/add", method={RequestMethod.POST, RequestMethod.OPTIONS})
    public ResponseEntity<Object> putDataToMicroservice(@RequestBody Map<String, Object> payload, @RequestHeader(value = "authorization") String authorizationHeader) throws Exception {

        // At this point you make a WebSocket request, is that right?
        doWebSocketRequest();

        // This poll call will block the current thread
        // until the WebSocket server responds,
        // or gives up waiting after the specified timeout.
        //
        // When the WebSocket server delivers a response,
        // the WS client implementation will execute the
        // @OnMessage annotated method in a thread
        // managed by the WS client itself.
        //
        // The @OnMessage method will pass the message
        // to this thread in the queue below.

        String message = queue.poll(30, TimeUnit.SECONDS);

        if (message == null) {
            // WebSocket timeout.
        }

        return ResponseEntity.ok("worked");
    }
}