HttpSession getAttribute() 返回 null

Posted 2023-02-16

【中文标题】HttpSession getAttribute() 返回 null

【英文标题】：HttpSession getAttribute() returning null

【发布时间】：2015-12-19 01:50:01

【问题描述】：

我正在尝试与 eclipse ide 进行 websocket 通信，当我运行我的代码时，我得到了 NullPointerException。我已经检查过了，getAttribute中的名称与bean中的名称相同

package ws;

import java.io.IOException;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;

import javax.websocket.server.ServerEndpoint;

import fundstarter.model.ConnectToRMIBean;

import javax.servlet.http.HttpSession;
import javax.websocket.*;

@ServerEndpoint(value="/ws", configurator = HandShake.class)
public class WebSocketAnnotation 

    private Session session;
    private ConnectToRMIBean sessionUser;
    private HttpSession httpSession;
    private static final Set<WebSocketAnnotation> myConnections = new CopyOnWriteArraySet<WebSocketAnnotation>();

    public WebSocketAnnotation() 

    

    @OnOpen
    public void start(Session session, EndpointConfig config) 

        this.session = session;
        this.httpSession = (HttpSession) config.getUserProperties().get(HttpSession.class.getName());
        myConnections.add(this);
        this.sessionUser = (ConnectToRMIBean) httpSession.getAttribute("RMIBean");
        //sendMessage("New message");
    

    @OnClose
    public void end() 
        // clean up once the WebSocket connection is closed
        myConnections.remove(this);
    

    @OnMessage
    public void receiveMessage(String message) 
        sendMessage(message);
        

    @OnError
    public void handleError(Throwable t) 
        t.printStackTrace();
        

    private void sendMessage(String text) 
        try 
            System.out.println("[WebSocketAnnot]RMIBean User Id -> " + this.sessionUser.getUserID());
            this.session.getBasicRemote().sendText(text);

         catch (IOException e) 
            try 
                this.session.close();
             catch (IOException e1) 
                e1.printStackTrace();
            
        
    

谁能告诉我我的错误是什么？

【参考方案1】：

我发现了错误。这是 HandShake 上 modifyHandshake 方法的拼写错误