哟哟哟，JAVA组装的聊天室，最简单的实现

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

public class VerySimpleChatServer {
    
    ArrayList  clientOutputStream;
    
    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 static void main(String[] args) {
        // TODO Auto-generated method stub
        new VerySimpleChatServer().go();
        }
    public void go() {
        clientOutputStream = new ArrayList();
        try {
            ServerSocket serverSock = new ServerSocket(5000);
            
            while(true) {
                Socket clientSocket = serverSock.accept();
                PrintWriter writer = new PrintWriter(clientSocket.getOutputStream());
                clientOutputStream.add(writer);
                
                Thread t = new Thread(new ClientHandler(clientSocket));
                t.start();
                System.out.println("service at port 5000...");
                System.out.println("got a connection...");
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    
    public void tellEveryone(String message) {
        
        Iterator it = clientOutputStream.iterator();
        while(it.hasNext()) {
            try {
                PrintWriter writer = (PrintWriter) it.next();
                writer.println(message);
                writer.flush();
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
        
    }

} 

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

import javax.swing.*;

import java.awt.*;
import java.awt.event.*;


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

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        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, 30);
        incoming.setLineWrap(true);
        incoming.setWrapStyleWord(true);
        incoming.setEditable(false);
        JScrollPane qScroller = new JScrollPane(incoming);
        qScroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
        qScroller.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        outgoing= new JTextField(20);
        JButton sendButton = new JButton("Send");
        sendButton.addActionListener(new SendButtonListener());
        mainPanel.add(qScroller);
        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 ev) {
            try {
                writer.println(outgoing.getText());
                writer.flush();
            } catch(Exception ex) {
                ex.printStackTrace();
            }
            outgoing.setText("");
            outgoing.requestDefaultFocus();
        }
    }
    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();
            }
        }
    }

}