Java中的多线程聊天服务器

Question

我想在Java中实现一个可以支持多个客户端的服务器 - 客户端套接字程序，但是当我的客户端连接到我的服务器时，执行多线程的类总是崩溃。

import java.io.*; 
import java.net.*; 
public class ClientWorker extends Thread{ 
    Socket cwsocket=null; 

    public ClientWorker(Socket cwsocket){ 
     super("ClientWorker"); 
     cwsocket=cwsocket; 
    } 

    public void run(){ 
     try { 
      PrintWriter out = new PrintWriter(cwsocket.getOutputStream(), true); 
      BufferedReader in = new BufferedReader(new InputStreamReader(cwsocket.getInputStream())); 

      String serverinput, serveroutput=""; 

      out.println(serveroutput); 

      while ((serverinput = in.readLine()) != null) { 
       out.println(serveroutput); 
       if (serveroutput.equals("Terminate")) 
        break; 
      } 
      out.close(); 
      in.close(); 
      cwsocket.close(); 

     } catch (IOException e) { 
      e.printStackTrace(); 
     } 
    } 
} 

每当我创建一个PrintWriter对象时，抛出一个NullPointerException异常，我不确定它为什么会继续发生。以下是我的服务器和客户端类。我究竟做错了什么？

import java.io.*; 
import java.net.*; 
public class Server { 

    public static void main(String[]args)throws IOException{ 
     ServerSocket serversocket=null; 
     final int PORT_NUM=4444; 
     boolean flag=true; 
     try{ 
      System.out.println("Listening for connection"); 
      serversocket=new ServerSocket(PORT_NUM); 
     }catch(IOException e){ 
      System.out.println("Could not listen to port: "+PORT_NUM); 
      System.exit(-1);  
     } 
     while(flag){ 
      new ClientWorker(serversocket.accept()).start(); 
     } 
     System.out.println("Terminating server..."); 
     serversocket.close(); 
    } 
} 

import java.io.*; 
import java.net.*; 
public class Client { 

    public static void main(String[] args){ 
     Socket socket=null; 
     PrintWriter out=null; 
     BufferedReader in=null; 
     BufferedReader userInputStream=null; 
     String IP="127.0.0.1"; 
     try{ 
      socket = new Socket(IP, 4444); 
      out = new PrintWriter(socket.getOutputStream(), true); 
      in = new BufferedReader(new InputStreamReader(socket.getInputStream())); 
     } catch (UnknownHostException e) { 
      System.out.println("Unknown host:" + IP); 
      System.exit(1); 
     } catch (IOException e) { 
      System.out.println("Cannot connect to server..."); 
      System.exit(1); 
     } 
     String userInput, fromServer; 
     try{   
      userInputStream = new BufferedReader(new InputStreamReader(System.in)); 
      while ((fromServer = in.readLine()) != null) { 
       System.out.println("Server: " + fromServer); 
       if (fromServer.equals("Terminate")) 
        break; 

       userInput = userInputStream.readLine(); 
       if (userInput != null) { 
         System.out.println("> " + userInput); 
         out.println(userInput); 
       } 
      } 
     }catch(IOException e){ 
      System.out.println("Bad I/O"); 
      System.exit(1); 
     } 
     try{ 
      out.close(); 
      in.close(); 
      userInputStream.close(); 
      socket.close(); 
      System.out.println("Terminating client..."); 
     }catch(IOException e){ 
      System.out.println("Bad I/O"); 
      System.exit(1); 
     }catch(Exception e){ 
      System.out.println("Bad I/O"); 
      System.exit(1); 
     } 
    } 
} 

Answer 1

在

public ClientWorker(Socket cwsocket){ 
     super("ClientWorker"); 
     cwsocket=cwsocket; 
    } 

你需要做的

 this.cwsocket=cwsocket; 

或重命名参数，因此不会遮盖同名的成员。