如何在jetty容器中设置JSR356 websockets

Question

我看到了很多关于如何使用某种嵌入式web服务器来设置JSR356 websockets的教程。

但我想将一些websockets添加到部署到独立jetty安装的现有WAR中，jetty jetty-9.2.3.v20140905，我在这方面找到的信息很少。我不知道是什么阻碍了它的工作。据我所知，带注释的服务器端点应该由jetty自动处理。

ServerEndpoint：

    @ServerEndpoint(value = "/myendpoint")
public class MyServerEndpoint {     
    private Logger logger = Logger.getLogger(this.getClass().getName());     

    @OnOpen 
    public void onOpen(Session s) {
        logger.info("Server Connected ... " + s.getId());
        s.getAsyncRemote().sendText("You are connected to the websocket server");   
    }        

    @OnMessage  
    public void onMessage(String message, Session session) {

        // Sent the message back to all connected users             
        logger.info("Server Session " + session + " Received string message " + message);

        for(Session s: session.getOpenSessions()) {     
            if (s.isOpen()) { 
                s.getAsyncRemote().sendText(message + " server response");
            }       
        }   
    }        

    @OnClose    
    public void onClose(Session session, CloseReason reason) {
        logger.info("Server Session " + session + " closed for reason " + reason);
    }   
}

ClientEndpoint：

    @ClientEndpoint
public class MyClientEndpoint {     
    private Logger logger = Logger.getLogger(this.getClass().getName());     

    @OnOpen 
    public void onOpen(Session s) {
        logger.info("Client Connected ... " + s.getId());
        s.getAsyncRemote().sendText("hello from the client!");  
    }        

    @OnMessage  
    public void onMessage(String message, Session session) {

        logger.info("Client Session " + session + " Received string message " + message);       

    }        

    @OnClose    
    public void onClose(Session session, CloseReason reason) {
        logger.info("Client Session " + session + " closed for reason " + reason);
    }   
}

下面是将客户机连接到服务器的代码(在一些现有方法中运行

    WebSocketContainer container = ContainerProvider.getWebSocketContainer();
    String uri = "ws://localhost:8080/myWar/myendpoint"; 
    container.connectToServer(MyClientEndpoint.class, URI.create(uri));

然而，启动jetty会在connectToServer行中显示一个错误

2014-10-30 12:26:58.658:WARN:oeja.ServletContainerInitializersStarter:main: 
org.eclipse.jetty.websocket.api.InvalidWebSocketException: Unable to instantiate websocket: class java.lang.Class
at   org.eclipse.jetty.websocket.jsr356.ClientContainer.newClientEndpointInstance(ClientContainer.java:311)
    at org.eclipse.jetty.websocket.jsr356.ClientContainer.connectToServer(ClientContainer.java:172)

我所能想到的就是URI不正确。如果jetty在8080上运行，我的.war名为myWar，我的端点名为myendpoint...is，那么不是正确的URI吗？

要“激活”服务器端点以侦听连接，是否需要执行一些额外的步骤？我肯定漏掉了什么明显的东西。

Answer 1

奇怪的是，你的错误信息。

org.eclipse.jetty.websocket.api.InvalidWebSocketException: 
  Unable to instantiate websocket: class java.lang.Class

意味着websocket实现被传递了一个原始的java.lang.Class来实例化。那是行不通的。

这也意味着没有尝试连接，因为WebSocket类本身非常糟糕，连接是不可能的。

下面是一个简短的(有效且有效的)示例，展示了它的用法。

package jetty.jsr356;

import java.io.IOException;
import java.net.URI;
import java.util.concurrent.CountDownLatch;

import javax.websocket.ClientEndpoint;
import javax.websocket.CloseReason;
import javax.websocket.CloseReason.CloseCodes;
import javax.websocket.ContainerProvider;
import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.WebSocketContainer;

@ClientEndpoint
public class TestClientAnnotatedClass
{
    private static CountDownLatch closeLatch = new CountDownLatch(1);

    @OnOpen
    public void onOpen(Session session)
    {
        System.out.println("@OnOpen - " + session);
        try
        {
            session.getBasicRemote().sendText("Rock it with Java WebSocket");
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }

    @OnMessage
    public void onMessage(Session session, String msg)
    {
        System.out.println("@OnMessage - ["+msg+"]");
        try
        {
            session.close(new CloseReason(CloseCodes.NORMAL_CLOSURE,"Thanks"));
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }

    @OnClose
    public void onClose(CloseReason close)
    {
        System.out.println("@OnClose - " + close);
        closeLatch.countDown();
    }

    public static void main(String[] args)
    {
        try
        {
            WebSocketContainer ws = ContainerProvider.getWebSocketContainer();

            ws.connectToServer(TestClientAnnotatedClass.class,new URI("ws://echo.websocket.org/?encoding=text"));
            closeLatch.await();
        }
        catch (Throwable t)
        {
            t.printStackTrace();
        }
    }
}

您将看到类似以下内容的输出

2014-10-30 11:34:19.197:INFO::main: Logging initialized @71ms
@OnOpen - WebSocketSession[websocket=JsrAnnotatedEventDriver[websocket=jetty.jsr356.TestClientAnnotatedClass@5cca5f2c],behavior=CLIENT,connection=WebSocketClientConnection@6a2e714b{IDLE}{f=Flusher[queueSize=0,aggregateSize=0,failure=null],g=Generator[CLIENT,validating],p=Parser@55465b1f[ExtensionStack,s=START,c=0,len=0,f=null,p=WebSocketPolicy@7e087bf5[behavior=CLIENT,maxTextMessageSize=65536,maxTextMessageBufferSize=32768,maxBinaryMessageSize=65536,maxBinaryMessageBufferSize=32768,asyncWriteTimeout=60000,idleTimeout=300000,inputBufferSize=4096]]},remote=WebSocketRemoteEndpoint@5f025277[batching=true],incoming=JsrAnnotatedEventDriver[websocket=jetty.jsr356.TestClientAnnotatedClass@5cca5f2c],outgoing=ExtensionStack[queueSize=0,extensions=[],incoming=org.eclipse.jetty.websocket.jsr356.JsrSession,outgoing=org.eclipse.jetty.websocket.client.io.WebSocketClientConnection]]
@OnMessage - [Rock it with Java WebSocket]
@OnClose - CloseReason[1000,Thanks]

Answer 2

Jetty使用反射创建带注释的客户端端点的实例(参见/jetty/websocket/jsr356/ClientContainer#newClientEndpointInstance())，但是Jetty无法以的方式实例化非静态内部类。实际的原因异常类似于java.lang.NoSuchMethodException: <pkg>.OuterClass$InnerClass.<init>()，但它被吞噬了。

解决方案:带注释的端点类不应该是嵌套或嵌套的静态(内部)类。