DataInputStream的Java Socket]实例打印继续null

Question

我正在使用Java Swing进行聊天室程序。

在客户端，我看到它没有从服务器端读取消息。

客户端的writeUTF()方法非常好，我在服务器端检查readUTF和writeUTF，这也非常好。

我认为问题是代码在客户端做为“Receiver”。

在线程的run()方法中，DataInputStream的实例dis具有连续的空值。

我很困惑..请给我一些帮助。

波纹管是我的客户端&服务器代码的一部分。

谢谢！

客户端代码

RoomBackground.java

public class RoomBackground { 

    private static String socket_server = "127.0.0.1"; 
    private static Socket chatSocket; 
    private static DataOutputStream dos; 
    private static DataInputStream dis; 
    private ChatReceiver chatReceiver; 

    public Socket getChatSocket() { 
     return chatSocket; 
    } 

    public static DataOutputStream getDos() { 
     return dos; 
    } 

    public RoomBackground() throws IOException { 
     chatSocket = new Socket(socket_server, 7777); 
     chatReceiver = new ChatReceiver(); 
     chatReceiver.start(); 

     dos = new DataOutputStream(chatSocket.getOutputStream()); 
     dis = new DataInputStream(chatSocket.getInputStream()); 
     dos.writeUTF(User.getUser().getUsername()); 
     dos.flush(); 
    } 
    class ChatReceiver extends Thread { 
     @Override 
     public void run(){ 
      try { 
       # PROBLEM CODE..... Allways "dis is null" 
       System.out.println("dis is " + dis); 

       # This line never executed. 
       while(dis != null) {  

        # some codes..... 

       } 
      } catch (IOException e) { 
       e.printStackTrace(); 
       System.out.println(e.toString()); 
      } catch (BadLocationException e) { 
       e.printStackTrace(); 
      } 
     } 
    } 
} 

RoomFrame.java

public class RoomFrame extends JFrame{ 

    private RoomBackground roomBackground; 

    public RoomFrame(int roomId) throws IOException { 
     chatField.addActionListener(new ActionListener() { 
      roomBackground = new RoomBackground(); 
      @Override 
      public void actionPerformed(ActionEvent e) { 
       String msg = chatField.getText() + "\n"; 
       try { 
        RoomBackground.getDos().writeUTF(msg); 

        # It works. 
        System.out.println("sent msg is " + msg); 
       } catch (IOException e1) { 
        e1.printStackTrace(); 
       } 
       chatField.setText(""); 
      } 
     }); 
    } 
} 

现在服务器代码。

服务器Background.java

public class ChatReceiver extends Thread { 

    private DataInputStream in; 
    private DataOutputStream out; 

    public ChatReceiver(Socket chatSocket) throws IOException { 

     out = new DataOutputStream(chatSocket.getOutputStream()); 
     in = new DataInputStream(chatSocket.getInputStream()); 

     nick = in.readUTF(); 
     addChatClient(nick, out);  
    } 

    @Override 
    public void run() { 
     try { 
      while(in!=null) { 
       chatMsg = in.readUTF(); 

       # It works ! 
       System.out.println("before send" + chatMsg); 
       sendMsg(chatMsg); 

       # It works too! 
       System.out.println("after send" + chatMsg); 
      } 
     }catch (IOException e) { 
      removeChatClient(nick); 
     } 
    } 
} 

Answer 1

当你开始在RoomBackground的dis对象ChatReceiver线程尚未初始化，这就是为什么它是null。一种解决方案可能是在ChatReceiver构造函数中初始化dis变量。