为什么用java编写的两台计算机之间的udp连接聊天程序总是显示socket closed阿?小弟在线等,谢了!

Question

除窗体之外主要就是这些了....:try {    
        sendsocket=new DatagramSocket(5001);//实例化DatagramSocket类作为输出端
           receivesocket=new DatagramSocket(5000);//实例化DatagramSocket类作为输入端
           online = !(sendsocket.isClosed());
     }
      catch(SocketException se){//异常捕获
         se.printStackTrace() ;
         System.exit(0);
     }
  }
  
  protected void processWindowEvent(WindowEvent e) {
    super.processWindowEvent(e);
    if (e.getID() == WindowEvent.WINDOW_CLOSING) {
      System.exit(0);
    }
  }
  public void waitforpackets(){//检测并接受对方发来的消息
    while(true){
        try{
             byte[]array=new byte[100];
              receivepacket=new DatagramPacket(array,array.length );
              receivesocket.receive(receivepacket);//接收
              textArea1.append("\nfrom "+receivepacket.getAddress() +":"+receivepacket.getPort()+" get:");
             byte data[]=receivepacket.getData() ;
              String received=new String(data,0);
              textArea1.append(received);
        }
        catch (IOException se){
                se.printStackTrace() ;
        }
    }
  }

Answer 1

import java.net.*;
import java.io.*;
import javax.swing.UIManager;
import java.awt.*;
public class ChatApp {
  boolean packFrame = false;  public ChatApp() {
    ChatFrame frame = new ChatFrame();
    if (packFrame) {
      frame.pack();
    }
    else {
      frame.validate();
    }
    //放置窗体在屏幕中央
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    Dimension frameSize = frame.getSize();
    if (frameSize.height > screenSize.height) {
      frameSize.height = screenSize.height;
    }
    if (frameSize.width > screenSize.width) {
      frameSize.width = screenSize.width;
    }
    frame.setLocation((screenSize.width - frameSize.width) / 2, (screenSize.height - frameSize.height) / 2);
    frame.setVisible(true);
    frame.waitforpackets();
  }  public static void main(String[] args) {
    try {
      UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
    }
    catch(Exception e) {
      e.printStackTrace();
    }
    new ChatApp();
  }
}import java.net.*;
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.lang.*;public class ChatFrame extends JFrame {
  JPanel contentPane;
  Label label1 = new Label();//发送消息
  Label label2 = new Label();//输入ip
  Label label3 = new Label();//输入端口标签
  Label label4 = new Label();//输出端口标签
  TextField textField1 = new TextField();//输入ip
  TextField textField2 = new TextField();//发送消息
  TextField textField3 = new TextField();//获得输入端口
  TextField textField4 = new TextField();//获得输出端口
  Button button1 = new Button();//发送消息
  Button button2 = new Button();//建立连接
  TextArea textArea1 = new TextArea();  boolean online = false;
  int portIn = 5000;//输入端口
  int portOut = 5001;//输出端口  DatagramPacket sendpacket,receivepacket;//声明发送和接收数据包
  DatagramSocket sendsocket,receivesocket;//声明发送和接收DatagramSocket
  public ChatFrame() {
    enableEvents(AWTEvent.WINDOW_EVENT_MASK);
    try {
      toInit();
    }
    catch(Exception e) {
      e.printStackTrace();
    }
  }
  
  private void toInit() throws Exception  {
    contentPane = (JPanel) this.getContentPane();
    label1.setText("发送信息：");
    label1.setBounds(new Rectangle(13, 100, 60, 21));
    contentPane.setLayout(null);
    this.setSize(new Dimension(363, 320));
    this.setTitle("二人聊天室");
    label2.setText("输入对方IP地址：");
    label2.setBounds(new Rectangle(12, 19, 109, 23));
    label3.setText("输入端口：");
    label3.setBounds(new Rectangle(12,58,55,22));
    label4.setText("输出端口：");
    label4.setBounds(new Rectangle(180,58,55,22));
    textField3.setText("5000");
    textField4.setText("5001");
    textField2.setText("210.77.26.60");    button1.setLabel("发送");
    button1.setBounds(new Rectangle(280, 100, 59, 21));
    button1.addActionListener(new java.awt.event.ActionListener() {
      public void actionPerformed(ActionEvent e) {
        button1_actionPerformed(e);
      }
    });
    button2.setLabel("连接");
    button2.setBounds(new Rectangle(280, 20, 59, 21));
    button2.addActionListener(new java.awt.event.ActionListener() {
      public void actionPerformed(ActionEvent e) {
        button2_actionPerformed(e);
      }
    });    textField4.setBounds(new Rectangle(240,58,90,22));
    textField3.setBounds(new Rectangle(70,58,90,22));
    textField2.setBounds(new Rectangle(123, 20, 120, 19));
textField1.setBounds(new Rectangle(76, 100, 190, 19));
    textArea1.setBounds(new Rectangle(11, 140, 333, 134));
    textArea1.setEditable(false);
    contentPane.add(label4, null);
    contentPane.add(label3, null);
    contentPane.add(label2, null);
    contentPane.add(label1, null);
    contentPane.add(textField1, null);
    contentPane.add(textField2, null);
    contentPane.add(textField3, null);
    contentPane.add(textField4, null);
    contentPane.add(textArea1, null);
    contentPane.add(button1, null);
    contentPane.add(button2,null);
    
    try {    
        sendsocket=new DatagramSocket(5001);//实例化DatagramSocket类作为输出端
           receivesocket=new DatagramSocket(5000);//实例化DatagramSocket类作为输入端
           online = !(sendsocket.isClosed());
     }
      catch(SocketException se){//异常捕获
         se.printStackTrace() ;
         System.exit(0);
     }
  }
  
  protected void processWindowEvent(WindowEvent e) {
    super.processWindowEvent(e);
    if (e.getID() == WindowEvent.WINDOW_CLOSING) {
      System.exit(0);
    }
  }
  public void waitforpackets(){//检测并接受对方发来的消息
    while(true){
        try{
             byte[]array=new byte[100];
              receivepacket=new DatagramPacket(array,array.length );
              receivesocket.receive(receivepacket);//接收
              textArea1.append("\nfrom "+receivepacket.getAddress() +":"+receivepacket.getPort()+" get:");
             byte data[]=receivepacket.getData() ;
              String received=new String(data,0);
              textArea1.append(received);
        }
        catch (IOException se){
                se.printStackTrace() ;
        }
    }
  }
  
  void button2_actionPerformed(ActionEvent e){//和对方建立连接
  
   String str2 = new String();
    String str3 = new String();
   str2 = textField3.getText();
    str3 = textField4.getText();
        
    if(str2.compareTo("")!=0&&str3.compareTo("")!=0){
    
     portIn = (int) Integer.parseInt(str2);
     portOut = (int) Integer.parseInt(str3);
    
    
     if(online){
     sendsocket.close();
     receivesocket.close();
     textArea1.append("\n formal connection closed");
     }
         
     try {
      textArea1.append("\n building a connection use the port defined...");
        sendsocket=new DatagramSocket(portOut);
           receivesocket=new DatagramSocket(portIn);
           textArea1.append("\n connection builded.");
     }
      catch(SocketException se){
         se.printStackTrace() ;
         System.exit(0);
     }
     online = !(sendsocket.isClosed());
    }
    
    
else
        textArea1.append("\nplease input ports and IP");
       
    }
  
  void button1_actionPerformed(ActionEvent e) {//发送消息到对方
       
        
        String str=textField2.getText();
        if(online){
         if(str.compareTo("")!=0 ){
        
            
             try {
            
                              
                 textArea1.append("\nto "+textField2.getText() +":"+portOut+" say: "+textField1.getText() );
                 String s=textField1.getText() ;
                 byte data[]=new byte[100];
                 s.getBytes(0,s.length() ,data,0);
                 sendpacket=new DatagramPacket(data,s.length() ,InetAddress.getByName(textField2.getText()),portOut);
                 sendsocket.send(sendpacket);
             }
             catch(IOException exc){
                exc.printStackTrace() ;
             }
        
         }
        
         }
        else textArea1.append("\nplease build a connection first!");
  }
}总是不能与指定ip的机器建立连接,我觉得程序应该没什么问题阿???

Answer 2

你的sendsocket没有connect(ip,port), 就去send, 当然socket closed
连接根本没建立!