LAMBDA不起作用在WebSocket的会议

Question

我只是遇到了一个奇特的小问题：

javax.websocket.Session session = //... 
// this works 
newSession.addMessageHandler(new MessageHandler.Whole<String>() { 

    @Override 
    public void onMessage(String message) { 
     MyWebSocket.this.onMessage(message); 
    } 
}); 
// these don't work 
newSession.addMessageHandler((MessageHandler.Whole<String>) MyWebSocket.this::onMessage); 
newSession.addMessageHandler((MessageHandler.Whole<String>) message -> MyWebSocket.this.onMessage(message)); 


void onMessage(String message) { 
    System.out.println(message); 
} 

有谁知道为什么lambda表达式不会在这种情况下工作吗？有没有编译错误，也不例外，什么都没有。该方法'的onMessage'只是不叫。

我使用Java 1.8.0_65和泰鲁斯参考实现1.9。

Answer 1

请参阅https://blogs.oracle.com/PavelBucek/entry/websocket_api_1_1_released

tldr;你必须使用Session#addMessageHandler(Class<T> clazz, MessageHandler.Whole<T> handler)

/** 
* Register to handle to incoming messages in this conversation. A maximum of one message handler per 
* native websocket message type (text, binary, pong) may be added to each Session. I.e. a maximum 
* of one message handler to handle incoming text messages a maximum of one message handler for 
* handling incoming binary messages, and a maximum of one for handling incoming pong 
* messages. For further details of which message handlers handle which of the native websocket 
* message types please see {@link MessageHandler.Whole} and {@link MessageHandler.Partial}. 
* Adding more than one of any one type will result in a runtime exception. 
* 
* @param clazz type of the message processed by message handler to be registered. 
* @param handler whole message handler to be added. 
* @throws IllegalStateException if there is already a MessageHandler registered for the same native 
*        websocket message type as this handler. 
*/ 
public void addMessageHandler(Class<T> clazz, MessageHandler.Whole<T> handler); 

为了使用lambda表达式作为消息左撇子。

Answer 2

从我的理解MessageHandler将需要是@FunctionalInterface允许lambda表达式在这里，情况并非如此。