客户端

import java.io.*;
import java.net.*;
import java.util.*;
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;


public class SimpleChatClient {
    JTextArea incoming;
    JTextField outgoing;
    BufferedReader reader;
    PrintWriter writer;
    Socket sock;

    public static void main(String[] args) {
        SimpleChatClient client = new SimpleChatClient();
        client.go();
    }

    public void go() {
        JFrame frame = new JFrame("Ludicrously Simple chat Client");
        JPanel mainPanel = new JPanel();
        incoming = new JTextArea(15, 50);
        incoming.setLineWrap(true);
        incoming.setWrapStyleWord(true);
        incoming.setEditable(true);
        JScrollPane qScrollPanel = new JScrollPane(incoming);
        qScrollPanel.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
        qScrollPanel.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        outgoing = new JTextField();
        JButton sendButton = new JButton("Send");
        sendButton.addActionListener(new SendButtonListener());
        mainPanel.add(qScrollPanel);
        mainPanel.add(outgoing);
        mainPanel.add(sendButton);
        setUpNetworking();

        Thread readerThread = new Thread(new IncomingReader());
        readerThread.start();

        frame.getContentPane().add(BorderLayout.CENTER, mainPanel);
        frame.setSize(400, 500);
        frame.setVisible(true);
    }

    private void setUpNetworking() {
        try {
            sock = new Socket("127.0.0.1", 5000);
            InputStreamReader streamReader = new InputStreamReader(sock.getInputStream());
            reader = new BufferedReader(streamReader);
            writer = new PrintWriter(sock.getOutputStream());
            System.out.println("networking established");
        } catch(IOException ex) {
            ex.printStackTrace();
        }
    }
    public class SendButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent ae) {
            try {
                writer.println(outgoing.getText());
                writer.flush();
            } catch(Exception e) {
                e.printStackTrace();
            }
            outgoing.setText("");
            outgoing.requestFocus();
        }
    }
    public class IncomingReader implements Runnable {
        public void run() {
            String message;
            try {
                while ((message = reader.readLine()) != null) {
                    System.out.println("read " + message);
                    incoming.append(message + "\n");
                }
            } catch(Exception ex) {
                ex.printStackTrace();
            }
        } 
    }
}
···
服务器端
···
import java.io.*;
import java.net.*;
import java.util.*;


public class VerySimpleChatServer {
    ArrayList clientOutputStreams;
    
    public static void main(String[] args) {
        new VerySimpleChatServer().go();
    }

    public class ClientHandler implements Runnable{
        BufferedReader reader;
        Socket sock;

        public ClientHandler(Socket ClientSocket) {
            try {
                sock = ClientSocket;
                InputStreamReader isReader = new InputStreamReader(sock.getInputStream());
                reader = new BufferedReader(isReader);
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }

        public void run() {
            String message;
            try {
                while ((message = reader.readLine()) != null) {
                    System.out.println("read " + message);
                    tellEveryone(message);
                }
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    } 

    public void go() {
        clientOutputStreams = new ArrayList();
        try {
                ServerSocket serverSocket = new ServerSocket(5000);

                while (true) {
                    Socket clientSocket = serverSocket.accept();
                    PrintWriter writer = new PrintWriter(clientSocket.getOutputStream());
                    clientOutputStreams.add(writer);

                    Thread t = new Thread(new ClientHandler(clientSocket));
                    t.start();
                    System.out.println("got a connection");
                }
                
            } catch (Exception ex) {
                    ex.printStackTrace();
            }
    }
 
    public void tellEveryone(String message) {
        Iterator it = clientOutputStreams.iterator();
        while (it.hasNext()) {
            try {
                PrintWriter writer = (PrintWriter) it.next();
                writer.println(message);
                writer.close();
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }
}
···