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

public class ChatServer {
	
	ServerSocket server = null;
	Collection cClient = new ArrayList();//裝執行緒的容器
	
	
	public ChatServer(int port) throws Exception {
		server = new ServerSocket(port);
	}
	
	public void startServer() throws Exception {
		while (true) {
			Socket s = server.accept();
			
			cClient.add(new ClientConn(s));
			System.out.println("NEW-CLIENT " + s.getInetAddress() + ":" + s.getPort());
			System.out.println("CLIENTS-COUNT: " + cClient.size() + "\n");
			
		}
	}

	//多執行緒
	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() {
			try {
				if (s != null) s.close();
				cClient.remove(this);
				System.out.println("A client out!");
				System.out.println("CLIENT-COUNT: " + cClient.size() + "\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(s.getInetAddress() + "-" + s.getPort() + ": " + str);
					for (Iterator it = cClient.iterator(); it.hasNext();) {
						ClientConn cc = (ClientConn) it.next();
						//if (this != cc) {
							cc.send(s.getInetAddress() + "-" + s.getPort() + ": " + str);
						//}
					}
					str = dis.readUTF();
					//send(str);
				}
				this.dispose();
			} catch (Exception e) {
				System.out.println("client quit");
				this.dispose();
			}
			
		}
	}
	
	public static void main(String[] args) throws Exception {
		ChatServer cs = new ChatServer(8888);
		cs.startServer();
	}
}
 

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

public class ChatClient extends Frame {
	TextArea ta = new TextArea();
	TextField tf = new TextField();
	Socket s = null;
	
	public void launchFrame() throws Exception {
		this.add(ta, BorderLayout.CENTER);
		this.add(tf, BorderLayout.SOUTH);
		tf.addActionListener(new ActionListener() {
				public void actionPerformed(ActionEvent ae) {
					try {
						String sSend = tf.getText();
						if (sSend.trim().length() == 0) {
							System.out.println("輸入為空!");
							return;
						}
						ChatClient.this.send(sSend);
						tf.setText("");
						ta.append("me: " + sSend + "\n");
					} catch (Exception e) {
						e.printStackTrace();
					}
				}
			}
		);
		
		this.addWindowListener(new WindowAdapter() {
				public void windowClosing(WindowEvent e) {
					System.exit(0);
				}
			}
		);
		setBounds(300,300,300,400);
		setVisible(true);
		ta.requestFocus();
	}
	
	
	
	public ChatClient() throws Exception {
		s = new Socket("39.108.12.42", 9050);
		launchFrame();
		(new Thread(new ReceiveThread())).start();
	}
	//向伺服器傳送資料
	public void send(String str) throws Exception {
		DataOutputStream dos = new DataOutputStream(s.getOutputStream());
		dos.writeUTF(str);
	}
	
	public void disconnect() throws Exception {
		s.close();
	}
	

	
	class ReceiveThread 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);
					ChatClient.this.ta.append(str + "\n");
					str = dis.readUTF();
				}
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}
	
	public static void main(String[] args) throws Exception {
		ChatClient cc = new ChatClient();
	}
}