Socket.accept（）抛出空指针异常

Question

我正在写一个单独的p2p文件共享程序，它将接受连接，并且也可以作为服务器本身。

及其在过程，但线：60

插座sock1 = tcpSocket.accept（）;

抛出一个空指针异常，我不知道什么是错的。试了一切。

import java.net.*; 
import java.io.*; 


public class echoer implements Runnable { 
    int i,backlog; 
    public Socket tcpClient= null; 
    public ServerSocket tcpSocket= null; 
    public echoer(int tcpPort, int udpPort, int backlog) { 
     try { 
      this.tcpSocket = new ServerSocket(tcpPort,backlog); 
      System.out.println("Server connected to "+ InetAddress.getLocalHost() + "on TCP port " + tcpPort + "and UDP port " + udpPort); 
      this.backlog= backlog; 
      listening(); 
     } 
     catch (SocketTimeoutException s) { 
      System.out.println("timeout"); 
     } 
     catch (IOException ioe) { 
      System.out.println("could not listen on port 10009"); 
      System.exit(-1); 
     } 
} 
public echoer() { 

} 
void listening(){ 
     try { 
       //i++; 
       tcpSocket.getInetAddress(); 
       System.out.println(); 

       //Thread t1= new Thread((Runnable) new AcceptInput()); 
       //t1.start(); 
       //tcpSocket.accept(); 
       //System.out.println("Connection accepted"); 
       //messaging(); 
       Thread t2 = new Thread((Runnable) new echoer()); 
       t2.start(); 
      } 
      catch (Exception e) { 
       System.out.println("Cannot accept connection"); 
      } 
     } 

public void Client(String addr, int port) throws IOException 
{ 
    System.out.println("address= "+ addr+ "port= "+ port); 
    tcpClient = new Socket(addr,port); 
} 
/*void messaging() { 
    System.out.println("Starting Thread"); 
    Thread t = new Thread((Runnable) new echoer()); 
    t.start(); 
}*/ 
public void run() { 
    while (true) { 
     try { 
      //System.out.println("Listening on "+ InetAddress.getLocalHost().getHostAddress() + "on TCP port " + tcpSocket.getLocalSocketAddress()); 
      Socket sock1= tcpSocket.accept(); 
      //Client(InetAddress.getLocalHost().getHostAddress(),tcpSocket.getLocalPort()); 
      System.out.println("Connection accepted"); 
      ObjectOutputStream out= new ObjectOutputStream(sock1.getOutputStream()); 
      //Now start the messaging thread nad pass this sock1 to tcpClient 
      /*String line; 
      System.out.println("Write a message"); 
      DataInputStream din= new DataInputStream(tcpClient.getInputStream()); 
      line= din.readUTF(); 
      if (line == null) { 
       din.close(); 
       tcpClient.close(); 
       } 
      System.out.println("Recvd message:" + line);*/ 
      if (sock1 != null) { 
      tcpSocket.close(); 
      } 
     } 
     catch (IOException o) { 
      System.out.println("Read Failed"); 
      } 
     } 
    } 

    /*catch (IOException i) { 
     System.out.println("Last statement"); 
    } 
}*/ 
public static void main(String[] args) { 
    new echoer(Integer.parseInt(args[0]),Integer.parseInt(args[1]),5); 

} 
} 

class AcceptInput implements Runnable { 
    String token; 
    public void run() { 
     BufferedReader br= new BufferedReader(new InputStreamReader(System.in)); 
     try { 
      token= br.readLine(); 
     if (token== "connect") { 
      System.out.print("Enter IP address: "); 
      BufferedReader ip= new BufferedReader(new InputStreamReader(System.in)); 
      //accept ip and port 
      // pass ip and port to tcpclient socket to initiate a connection 
     } 
    } catch (IOException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 

} 

}

Answer 1

这里是当前的问题，你叫new Thread((Runnable) new echoer())，这开始你的线程。

但是，这会调用当前没有实际代码的echoer的默认空构造函数！

所以，即使你构建插座一次，你这样做之后，你只需创建echoer的新实例所有新的插座和对

调用run()这意味着，在运行所有插槽都为空，因为他们从未设置，因此通过NullPointerException当您尝试使用它们。