Java TCP实现多用户群聊天，每个客户端连接时输入自己用户名，服务端广播消息时在信息前标注哪一用户发出，请给出相应的服务器和客户端代码

服务器端代码：

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

public class ChatServer {
    private static ArrayList<PrintWriter> clients = new ArrayList<>();

    public static void main(String[] args) {
        try {
            ServerSocket serverSocket = new ServerSocket(8888);
            System.out.println("Chat server started.");

            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("Client connected from " + socket.getInetAddress().getHostAddress());
                new ClientHandler(socket).start();
            }

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

    private static class ClientHandler extends Thread {
        private Socket socket;
        private BufferedReader in;
        private PrintWriter out;
        private String username;

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

        @Override
        public void run() {
            try {
                in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                out = new PrintWriter(socket.getOutputStream(), true);

                // Ask for username
                out.println("Enter your username:");
                username = in.readLine();
                System.out.println(username + " joined the chat.");

                // Add client to list of clients
                synchronized (clients) {
                    clients.add(out);
                }

                // Broadcast message to all clients
                broadcastMessage(username + " joined the chat.");

                // Read messages from client and broadcast to all clients
                String message;
                while ((message = in.readLine()) != null) {
                    System.out.println(username + ": " + message);
                    broadcastMessage(username + ": " + message);
                }

            } catch (IOException e) {
                System.out.println(username + " left the chat.");
            } finally {
                // Remove client from list of clients
                synchronized (clients) {
                    clients.remove(out);
                }

                // Broadcast message to all clients
                broadcastMessage(username + " left the chat.");

                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        private void broadcastMessage(String message) {
            synchronized (clients) {
                for (PrintWriter client : clients) {
                    client.println(message);
                }
            }
        }
    }
}

客户端代码：

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

public class ChatClient {
    public static void main(String[] args) {
        try {
            Socket socket = new Socket("localhost", 8888);
            System.out.println("Connected to chat server.");

            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
            Scanner scanner = new Scanner(System.in);

            // Enter username
            System.out.print("Enter your username: ");
            String username = scanner.nextLine();
            out.println(username);

            // Read messages from server
            new Thread(() -> {
                try {
                    String message;
                    while ((message = in.readLine()) != null) {
                        System.out.println(message);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }).start();

            // Send messages to server
            String message;
            while (true) {
                message = scanner.nextLine();
                out.println(message);
            }

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

运行以上代码后，可以启动多个客户端与服务器进行连接，每个客户端连接时输入自己的用户名，服务端会在广播消息时在信息前标注哪一用户发出。