服务器端程序：

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;
			System.out.println("端口已开启,占用8888端口号....");
		} 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);
			}
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				ss.close();
			} catch (IOException e) {
				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！");
			}
		}

		public void run() {
			try {
				while (bConnected) {
					String str = dis.readUTF();
					System.out.println("------------来自本地服务器:" + str);
					for (int i = 0; i < clients.size(); i++) {
						Client c = clients.get(i);
						c.send(str);
					}
				}
			} 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();
					}

				} catch (IOException e1) {
					e1.printStackTrace();
				}

			}
		}
	}
}

客户端程序：

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

/**
 * @author Michael Huang
 * 
 */
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(8888);
	}

	public void launchFrame(int port) {
		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(port);

		tRecv.start();
	}

	public void connect(int port) {
		try {
			s = new Socket("127.0.0.1", port);
			dos = new DataOutputStream(s.getOutputStream());
			dis = new DataInputStream(s.getInputStream());
			System.out.println("~~~~~~~~连接成功~~~~~~~~!");
			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();
			tfTxt.setText("");

			try {
				dos.writeUTF(str);
				dos.flush();
			} catch (IOException e1) {
				e1.printStackTrace();
			}

		}

	}

	private class RecvThread implements Runnable {

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

		}

	}
}

Java socket长连接代码实现