采用UDP协议，编写一个Java网络应用程序，该应用分服务器端程序和客户端程序两部分。客户端指定一个服务器上的文件名，让服务器发回该文件的内容，或者提示文件不存在。（20分）（服务端程序和客户端

1、 采用UDP协议，编写一个Java网络应用程序，该应用分服务器端程序和客户端程序两部分。客户端指定一个服务器上的文件名，让服务器发回该文件的内容，或者提示文件不存在。（20分）（服务端程序和客户端程序分别命名为Server.java和Client.java）

这是第四届ITAT大赛B卷第6题！

服务器端：

import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.*;
import java.net.*;

public class N4BT6 extends Frame
{
DatagramSocket socket ;
DatagramPacket packet ;

byte[] buf ;
File file ;
FileInputStream input;
String message = "该文件不存在";
TextArea text;
public N4BT6(String title)
{
super(title);
text = new TextArea(6,4);
add(text);
setSize(400, 300);
setVisible(true);
addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
dispose();
}
});

buf = new byte[1024];
try
{
socket = new DatagramSocket(1230);
packet = new DatagramPacket(buf, buf.length);
socket.receive(packet);
file = new File(new String(packet.getData()));
socket = new DatagramSocket();
}
catch (Exception e)
{

e.printStackTrace();
}


if(file.exists())
{
try
{
buf = new byte[(int)file.length()];//由于下面的都重新实例化了，buf要先写，否则用到的buf就是前面接收时的buf
packet = new DatagramPacket(buf,buf.length,InetAddress.getLocalHost(),1234);
input = new FileInputStream(file);
input.read(buf);
socket.send(packet);
}
catch (IOException e)
{
e.printStackTrace();
}
}
else
{
try
{
packet = new DatagramPacket(message.getBytes(),message.getBytes().length,
InetAddress.getLocalHost(),1234);
socket.send(packet);
}
catch (Exception e)
{
e.printStackTrace();
}
}

}
public static void main(String[] args)
{
new N4BT6("Server");
}
}
客户端：

//ChatClient.java

import java.awt.*; import java.awt.event.*; import java.io.*; import java.net.*;

public class ChatClient extends Frame { Socket s = null; DataOutputStream dos = null; DataInputStream dis = null; private boolean bConnected = false;

TextField tfTxt = new TextField();

TextArea taContent = new TextArea(); Thread tRecv = new Thread(new RecvThread());

public static void main(String[] args) { new ChatClient().launchFrame(); }

public void launchFrame() { setLocation(400, 300); this.setSize(300, 300); add(tfTxt, BorderLayout.SOUTH); add(taContent, BorderLayout.NORTH); pack(); this.addWindowListener(new WindowAdapter() {

@Override public void windowClosing(WindowEvent arg0) { disconnect(); System.exit(0); } }); tfTxt.addActionListener(new TFListener()); setVisible(true); connect(); tRecv.start(); } public void connect() { try { s = new Socket("127.0.0.1", 8888); dos = new DataOutputStream(s.getOutputStream()); dis = new DataInputStream(s.getInputStream()); System.out.println("connected!"); bConnected = true; } catch (UnknownHostException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } public void disconnect() { try { dos.close(); dis.close(); s.close(); } catch (IOException e) { e.printStackTrace(); } } private class TFListener implements ActionListener {

public void actionPerformed(ActionEvent e) { String str = tfTxt.getText().trim(); //taContent.setText(str); tfTxt.setText(""); try { //System.out.println(s); dos.writeUTF(str); dos.flush(); //dos.close(); } catch (IOException e1) { e1.printStackTrace(); } } } private class RecvThread implements Runnable {

public void run() { try { while(bConnected) { String str = dis.readUTF(); //System.out.println(str); taContent.setText(taContent.getText() + str + '\n'); } } catch (SocketException e) { System.out.println("退出了，bye!"); } catch (EOFException e) { System.out.println("推出了，bye - bye!"); } catch (IOException e) { e.printStackTrace(); } } } }

//ChatServer.java

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

public class ChatServer { boolean started = false; ServerSocket ss = null; List<Client> clients = new ArrayList<Client>(); public static void main(String[] args) { new ChatServer().start(); } public void start() { try { ss = new ServerSocket(8888); started = true; } catch (BindException e) { System.out.println("端口使用中...."); System.out.println("请关掉相关程序并重新运行服务器！"); System.exit(0); } catch (IOException e) { e.printStackTrace(); } try { while(started) { Socket s = ss.accept(); Client c = new Client(s); System.out.println("a client connected!"); new Thread(c).start(); clients.add(c); //dis.close(); } } catch (IOException e) { e.printStackTrace(); } finally { try { ss.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } class Client implements Runnable { private Socket s; private DataInputStream dis = null; private DataOutputStream dos = null; private boolean bConnected = false; public Client(Socket s) { this.s = s; try { dis = new DataInputStream(s.getInputStream()); dos = new DataOutputStream(s.getOutputStream()); bConnected = true; } catch (IOException e) { e.printStackTrace(); } } public void send(String str) { try { dos.writeUTF(str); } catch (IOException e) { clients.remove(this); System.out.println("对方退出了！我从List里面去掉了！"); //e.printStackTrace(); } } public void run() { try { while(bConnected) { String str = dis.readUTF(); System.out.println(str); for(int i=0; i<clients.size(); i++) { Client c = clients.get(i); c.send(str); //System.out.println(" a string send !"); } } } catch (EOFException e) { System.out.println("Client closed!"); } catch (IOException e) { e.printStackTrace(); } finally { try { if(dis != null) dis.close(); if(dos != null) dos.close(); if(s != null) { s.close(); //s = null; } } catch (IOException e1) { e1.printStackTrace(); } } } } }

这里使用tcp协议编写，不过你可以当做参考。

先运行CharServer.java 然后运行ChatClient.java.

可以同时运行多个ChatClient.java

可以实现简单的聊天功能