Socket

ChatServer:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ChatServer
{
    private static final int PORT = 8080; 
    private static List<Socket> list;
    private ExecutorService exec;
    private ServerSocket server;

    public static void main(String[] args) 
    {
        new ChatServer().start();
    }
    
    public ChatServer()
    {
        list = new ArrayList<Socket>(); 
        exec = Executors.newCachedThreadPool();
        try 
        {
            server = new ServerSocket(PORT);
        } 
        catch (IOException e) 
        {
            e.printStackTrace();
        }
    }

    public void start()
    {
        System.out.println("The server has started.");
        Socket client = null;
        while (true) 
        {
            try 
            {
                client = server.accept();
                list.add(client);
                exec.execute(new ChatTask(client));
            } 
            catch (IOException e) 
            {
                e.printStackTrace();
            }
        }
    }

    static class ChatTask implements Runnable 
    {
        private Socket socket;
        private BufferedReader br;
        private PrintWriter pw;
        private String msg;

        public ChatTask(Socket socket) throws IOException 
        {
            this.socket = socket;
            br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            msg = "[" + this.socket.getInetAddress() + "]enter the chat room!There are ["+ list.size() + "] people.";
            sendMessage();
        }

        public void run() 
        {
            try 
            {
                while ((msg = br.readLine()) != null) 
                {
                    if (msg.trim().equals("bye")) 
                    {
                        list.remove(socket);
                        br.close();
                        pw.close();
                        msg = "[" + socket.getInetAddress() + "] leave chat room!There are [" + list.size() + "] people.";
                        socket.close();
                        sendMessage();
                        break;
                    } 
                    else 
                    {
                        msg = "[" + socket.getInetAddress() + "] says：" + msg;
                        sendMessage();
                    }
                }
            } 
            catch (IOException e) 
            {
                e.printStackTrace();
            }
        }

        private void sendMessage() throws IOException 
        {
            System.out.println(msg);
            for (Socket client : list) 
            {
                pw = new PrintWriter(client.getOutputStream(), true);
                pw.println(msg);
            }
        }
    }
}

CharClient:

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ChatClient 
{
    private static final int PORT = 8080;
    private static ExecutorService exec;

    public static void main(String[] args) throws Exception 
    {
        new ChatClient().start();
    }

    public ChatClient() 
    {
        exec = Executors.newCachedThreadPool();
    }
    
    public void start()
    {
        try 
        {
            Socket socket = new Socket("127.0.0.1", PORT);
            exec.execute(new Sender(socket));
            System.out.println("[" + socket.getInetAddress() + "] Welcome to the chat room!");
            BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String msg = null;
            while ((msg = br.readLine()) != null) 
            {
                System.out.println(msg);
            }
        } 
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

    static class Sender implements Runnable 
    {
        private Socket socket;

        public Sender(Socket socket) 
        {
            this.socket = socket;
        }

        public void run() 
        {
            try 
            {
                BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
                PrintWriter pw = new PrintWriter(socket.getOutputStream(), true);
                String msg = null;
                while (true) 
                {
                    msg = br.readLine();
                    pw.println(msg);
                    if (msg.trim().equals("bye")) 
                    {
                        pw.close();
                        br.close();
                        exec.shutdownNow();
                        break;
                    }
                }
            } 
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
    }
}