//本代码参考于马士兵的代码，做了一些简单的改动，例如获取主机名称好让用户知道那句话是谁发的，Swing方面基本上全改了，关键地方加了我所理解的注释，关键线程方面的代码基本上用马老师的

//服务器端代码

import java.awt.FlowLayout;

import java.io.DataInputStream;

import java.io.DataOutputStream;

import java.io.IOException;

import java.net.ServerSocket;

import java.net.Socket;

import java.util.ArrayList;

import java.util.Collection;

import java.util.Iterator;

import javax.swing.JFrame;

import javax.swing.JScrollPane;

import javax.swing.JTextArea;

public class QLServer extends JFrame{

public JTextArea jtextarea = null;

public void lanuchFrame(String str){

this.setName(str);

init();

}

private void init() {

setLayout(new FlowLayout());

jtextarea =new JTextArea(20, 17);

jtextarea.setLineWrap(true);

jtextarea.setEditable(false);

this.getContentPane().add(new JScrollPane(jtextarea));

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

setSize(200,400);

setLocationRelativeTo(null);

setResizable(false);

}

ServerSocket server = null;

Collection cClients = new ArrayList();//加个泛型

public void startServer() throws IOException{

while(true){

Socket s = server.accept();

cClients.add(new ClientConn(s));

jtextarea.append("new client login" + s.getInetAddress() + ":" + s.getPort()+"\n");

}

}

public QLServer(int port,String str) throws IOException{

server = new ServerSocket(port);

lanuchFrame(str);

}

class ClientConn implements Runnable

{

Socket s = null;

public ClientConn(Socket s)

{

this.s = s;

(new Thread(this)).start();

}

public void send(String str) throws IOException

{

DataOutputStream dos = new DataOutputStream(s.getOutputStream());

dos.writeUTF(str);

}

public void dispose()//客户端下线

{

try {

if (s != null) s.close();

cClients.remove(this);

jtextarea.append("A client out! \n");

jtextarea.append("client count: " + cClients.size() + "\n\n");

}

catch (Exception e)

{

e.printStackTrace();

}

}

public void run()

{

try {

DataInputStream dis = new DataInputStream(s.getInputStream());

String str = dis.readUTF();

while(str != null && str.length() !=0)

{

System.out.println(str);

for(Iterator it = cClients.iterator(); it.hasNext(); )

{

ClientConn cc = (ClientConn)it.next();

if(this != cc)

{

cc.send(str+" "+s.getInetAddress().getHostName());

}

}

str = dis.readUTF();//少了这句话会无限输出

//send(str);

}

this.dispose();

}

catch (Exception e)

{

this.dispose();

}

}

}

public static void main(String[] args) {

try {

QLServer qlserver = new QLServer(8888,"QLServer");

qlserver.startServer();

} catch (IOException e) {

e.printStackTrace();

}

}

}===============================

import java.awt.FlowLayout;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import java.io.BufferedReader;

import java.io.DataInputStream;

import java.io.DataOutputStream;

import java.io.IOException;

import java.io.InputStreamReader;

import java.net.InetAddress;

import java.net.Socket;

import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JScrollPane;

import javax.swing.JTextArea;

//客户端代码

public class QLClient extends JFrame implements ActionListener{

public JTextArea jtextarea1 = null;

public JTextArea jtextarea2 = null;

public JButton button = null;

Socket s =null;

public void launchFrame(String str){

this.setName(str);

init();

}

public QLClient(String str) throws IOException{

launchFrame(str);

s = new Socket("127.0.0.1",8888);//哪台电脑做服务器，IP地址改成那台机子的IP

(new Thread(new ServeConn())).start();

}

private void init() {

setLayout(new FlowLayout());

jtextarea1 =new JTextArea(17, 16);

jtextarea2 =new JTextArea(4, 16);

jtextarea1.setLineWrap(true);

jtextarea1.setEditable(false);

jtextarea2.setLineWrap(true);

button = new JButton("发送");

button.addActionListener(this);//绑定button事件

this.getContentPane().add(new JScrollPane(jtextarea1));

this.getContentPane().add(new JScrollPane(jtextarea2));

add(button);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

setSize(200,470);

setLocationRelativeTo(null);

setResizable(false);

}

public void send(String str) throws IOException{

DataOutputStream dos = new DataOutputStream(s.getOutputStream());

dos.writeUTF(str);

}

public void actionPerformed(ActionEvent e) {

if(e.getSource()==button){

String sendStr = jtextarea2.getText();

if(sendStr.trim().length()==0){

return;

}

try {

this.send(sendStr);

jtextarea2.setText("");

InetAddress a;

a = InetAddress.getLocalHost();

String hostname = a.getHostName();

jtextarea1.append(sendStr+"("+hostname+")"+"\n");

} catch (IOException e1) {

// TODO Auto-generated catch block

e1.printStackTrace();

}

}

}

class ServeConn implements Runnable{

public void run() {

if(s == null) return;

try {

DataInputStream dis = new DataInputStream(s.getInputStream());

String str = dis.readUTF();

while (str != null && str.length() != 0)

{

//System.out.println(str);

QLClient.this.jtextarea1.append(str + "\n");//内部类用外类中的变量或方法加外类名

str = dis.readUTF();

}

}

catch (Exception e)

{

e.printStackTrace();

}

}

}

//main主函数入口

public static void main(String[] args) throws IOException {

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

QLClient qlclient = new QLClient("QLClient");

String str = br.readLine();

while(str!=null&&str.length()!=0){

qlclient.send(str);

str = br.readLine();//防止死循环

}

qlclient.s.close();

}

} 以上代码供参考，关于异常基本上没有处理，所以操作顺序不对可能会出现异常。