在上面代码的基础上实现一对多

好的，以下是在上面代码的基础上实现一对多通信的 JAVA 代码示例：

服务端代码：

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

public class Server {
    private static final int PORT = 9999;
    private static Set<Socket> clients = new HashSet<>();

    public static void main(String[] args) {
        try {
            ServerSocket serverSocket = new ServerSocket(PORT);
            System.out.println("服务端已启动，等待客户端连接...");

            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("客户端已连接：" + socket.getInetAddress().getHostAddress());
                clients.add(socket);
                new Thread(new ServerHandler(socket)).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    static class ServerHandler implements Runnable {
        private Socket socket;
        private BufferedReader reader;
        private PrintWriter writer;

        public ServerHandler(Socket socket) {
            try {
                this.socket = socket;
                this.reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                this.writer = new PrintWriter(socket.getOutputStream(), true);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void run() {
            try {
                while (true) {
                    String message = reader.readLine();
                    if (message == null) {
                        break;
                    }
                    System.out.println("客户端说：" + message);
                    broadcast(message);
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    reader.close();
                    writer.close();
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        public void broadcast(String message) {
            for (Socket client : clients) {
                try {
                    PrintWriter pw = new PrintWriter(client.getOutputStream(), true);
                    pw.println("客户端说：" + message);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

客户端代码：

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

public class Client {
    public static void main(String[] args) {
        try {
            Socket socket = new Socket("localhost", 9999);

            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);

            BufferedReader consoleReader = new BufferedReader(new InputStreamReader(System.in));

            new Thread(() -> {
                try {
                    while (true) {
                        String response = reader.readLine();
                        System.out.println(response);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }).start();

            while (true) {
                System.out.print("请输入消息：");
                String message = consoleReader.readLine();
                writer.println(message);
            }

            //reader.close();
            //writer.close();
            //socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

以上是一个简单的基于 SOCKET 的局域网一对多通信的 JAVA 代码示例。在实际开发过程中，还需要考虑异常处理、线程安全、协议设计等问题，并根据具体需求进行功能扩展。