//服务端
 import java.awt.*;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
 import java.io.*;
 import java.net.*;
 import java.security.Timestamp;
 import java.util.*;
 import java.util.prefs.BackingStoreException;

 import javax.swing.*;

 public class IServer extends JFrame {
     private static long  time1;
     private static    long  time2;
     private JPanel jp = new JPanel();
     private JTextArea jta = new JTextArea();
     private JScrollPane jsp = null;
     private JButton jb = new JButton("发送");
     private JTextField jtf = new JTextField(30);
     private ServerSocket server;
     private Socket socket;
     DataOutputStream dos;
     DataInputStream dis;
     public IServer() throws IOException
     {
         Toolkit t = Toolkit.getDefaultToolkit();
         Dimension Size =t.getScreenSize();
         int width =  Size.width;
         int height = Size.height;
         setLocationByPlatform(true);
         jsp = new JScrollPane(jta);
         this.setTitle("发送方");
         this.setSize(600, 500);
         this.setBounds((width - 600) / 2,
                 (height - 500) / 2, 600,500);
         jp.add(jtf);
         jp.add(jb);
         this.add(jsp, BorderLayout.CENTER);
         this.add(jp, BorderLayout.SOUTH);
         jta.setCaretPosition(jta.getDocument().getLength());// 设置滚动条自动滚动
         this.setVisible(true);
         this.setAlwaysOnTop(true);
         server = new ServerSocket(9000);
         socket= server.accept();
         this.setDefaultCloseOperation(EXIT_ON_CLOSE);
         dos = new DataOutputStream(socket.getOutputStream());
         dis =new DataInputStream(socket.getInputStream());
         jb.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent event){
                 try {
                     Send();
                 } catch (InterruptedException | IOException e) {
                     // TODO Auto-generated catch block
                     e.printStackTrace();
                 }
             }
         });
     }
     public static void main(String[] args) throws IOException, InterruptedException
     {
             new IServer();
     }
     public void Send() throws InterruptedException, IOException
     {
         String info = jtf.getText();
         jtf.setText("");
         char[] Msg = info.toCharArray();
         dos.write(Msg.length);
         for(int i=0;i<Msg.length;i++)
         {
             Random random=new java.util.Random();                        //实现数据帧错传，以随机数的概率来实现
             int result=random.nextInt(21);
             if(result>=4)
             {
                 if (jta.getText() == null || "".equals(jta.getText())) {
                     jta.append("Sending...:" + Msg[i]);
                 } else {
                     jta.append("\r\nSending...:" + Msg[i]);
                 }
                 dos.writeChar(Msg[i]);                                    //发送数据帧
                 time1 = System.currentTimeMillis();                        //设置超时计时器
             }
             else
             {
                 if (jta.getText() == null || "".equals(jta.getText())) {
                     jta.append("Sending...:" + Msg[i]);
                 } else {
                     jta.append("\r\nSending...:" + Msg[i]);
                 }
                 dos.writeChar('η');                                        //发送数据帧
                 time1 = System.currentTimeMillis();                         //设置超时计时器
             }
             int c = dis.readInt();                                        //接受客户端确认帧
             time2 = System.currentTimeMillis();
             long time = time2-time1;
             //System.out.println("接收所用时间："+time);
             if(time<500)                                                        //确认帧未超时
             {
                 if(c==i+2)                                                    //确认帧正确，传输成功，准备传输下一个帧
                 {
                     if(i<Msg.length-1)
                     {
                         if (jta.getText() == null || "".equals(jta.getText())) {
                             jta.append("Receive:" + c);
                         } else {
                             jta.append("\r\nReceive:" + c);
                         }
                         //System.out.println("接收方返回帧："+c+"  第"+(i+1)+"号帧传输成功！");
                     }
                     else
                     {
                         if (jta.getText() == null || "".equals(jta.getText())) {
                             jta.append("Receive:" + (i+2)+"数据传输成功！");
                         } else {
                             jta.append("\r\nReceive:" + (i+2)+"数据传输成功！");
                             jta.setEnabled(false);

                         }
                         //System.out.println("第"+(i+1)+"号帧传输成功！");
                         //System.out.println("数据传输成功！");
                         server.close();
                     }
                 }
                 else if(c==-2)                                                        //确认帧出错，超时重传
                 {
                     if (jta.getText() == null || "".equals(jta.getText())) {
                         jta.append("Receive:数据帧出错，丢弃等待....."+
                                 "确认帧接收超时，重新发送"+(i+1)+"帧");
                     } else {
                         jta.append("\r\nReceive:Receive:数据帧出错，丢弃等待....."
                     +"确认帧接收超时，重新发送"+(i+1)+"帧");
                     }
                     //System.out.println("数据帧出错，丢弃等待.....");
                     Thread.sleep(300);
                     //System.out.println("确认帧接收超时，重新发送"+(i+1)+"帧");
                     i=i-1;
                 }
             }
             else//超时，重传
             {
                 if (jta.getText() == null || "".equals(jta.getText())) {
                     jta.append("Receive:" +"确认帧接收超时，重新发送"+(i+1)+"帧");
                 } else {
                     jta.append("\r\nReceive:" + "确认帧接收超时，重新发送"+(i+1)+"帧");
                 }
                 //System.out.println("确认帧接收超时，重新发送"+(i+1)+"帧");
                 i=i-1;
             }
         }
     }
 }