用Java 编写一个基于socket的简易聊天程序。所编写的程序应具有如下功能： 1.具有点对点通信功能，任意客户端之间能够发送消息； 2.具有群组通信功能，客户端能够向组内成员同时发送消息，其他组成员不能收到； 3.具有广播功能，客户端能够向所有其他成员广播消息

好的，下面是代码实现：

1. 建立服务端

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

public class Server {
    public static void main(String[] args) {
        try {
            ServerSocket serverSocket = new ServerSocket(8888);
            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，IP地址为：" + socket.getInetAddress());

                // 创建线程处理客户端请求
                ServerThread serverThread = new ServerThread(socket);
                serverThread.start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class ServerThread extends Thread {
    private Socket socket;

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

    @Override
    public void run() {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));

            while (true) {
                String message = reader.readLine();
                if (message == null) {
                    continue;
                }

                // 广播消息
                if (message.equals("broadcast")) {
                    String broadcastMessage = reader.readLine();
                    broadcast(socket, broadcastMessage);
                }
                // 群组消息
                else if (message.equals("group")) {
                    String groupName = reader.readLine();
                    String groupMessage = reader.readLine();
                    group(groupName, socket, groupMessage);
                }
                // 点对点消息
                else {
                    String toUser = message;
                    String privateMessage = reader.readLine();
                    toUser(toUser, socket, privateMessage);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 广播消息
    private void broadcast(Socket fromSocket, String message) throws IOException {
        for (Socket socket : ServerUtils.getSockets()) {
            if (socket != fromSocket) {
                BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
                writer.write("广播消息：" + message + "\n");
                writer.flush();
            }
        }
    }

    // 群组消息
    private void group(String groupName, Socket fromSocket, String message) throws IOException {
        for (Socket socket : ServerUtils.getGroupSockets(groupName)) {
            if (socket != fromSocket) {
                BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
                writer.write("群组消息：" + message + "\n");
                writer.flush();
            }
        }
    }

    // 点对点消息
    private void toUser(String toUser, Socket fromSocket, String message) throws IOException {
        Socket toSocket = ServerUtils.getSocket(toUser);
        if (toSocket != null) {
            BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(toSocket.getOutputStream()));
            writer.write("点对点消息：" + message + "\n");
            writer.flush();
        } else {
            BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(fromSocket.getOutputStream()));
            writer.write("用户不存在\n");
            writer.flush();
        }
    }
}

2. 建立客户端

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

public class Client {
    private static Socket socket;

    public static void main(String[] args) {
        try {
            socket = new Socket("localhost", 8888);

            // 创建线程接收服务端消息
            ClientThread clientThread = new ClientThread(socket);
            clientThread.start();

            // 输入用户名
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            System.out.print("请输入用户名：");
            String username = reader.readLine();

            // 循环发送消息
            while (true) {
                System.out.println("请输入指令（1.点对点消息 2.群组消息 3.广播消息）：");
                int command = Integer.parseInt(reader.readLine());
                switch (command) {
                    // 点对点消息
                    case 1:
                        System.out.print("请输入要发送的用户名：");
                        String toUser = reader.readLine();
                        System.out.print("请输入要发送的消息：");
                        String privateMessage = reader.readLine();
                        sendPrivateMessage(toUser, privateMessage, username);
                        break;
                    // 群组消息
                    case 2:
                        System.out.print("请输入要发送的组名：");
                        String groupName = reader.readLine();
                        System.out.print("请输入要发送的消息：");
                        String groupMessage = reader.readLine();
                        sendGroupMessage(groupName, groupMessage, username);
                        break;
                    // 广播消息
                    case 3:
                        System.out.print("请输入要发送的消息：");
                        String broadcastMessage = reader.readLine();
                        sendBroadcastMessage(broadcastMessage, username);
                        break;
                    default:
                        System.out.println("无效指令");
                        break;
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 发送点对点消息
    private static void sendPrivateMessage(String toUser, String message, String fromUser) throws IOException {
        BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
        writer.write(toUser + "\n");
        writer.write(message + "\n");
        writer.flush();

        BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        String response = reader.readLine();
        System.out.println(response);
    }

    // 发送群组消息
    private static void sendGroupMessage(String groupName, String message, String fromUser) throws IOException {
        BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
        writer.write("group\n");
        writer.write(groupName + "\n");
        writer.write(message + "\n");
        writer.flush();
    }

    // 发送广播消息
    private static void sendBroadcastMessage(String message, String fromUser) throws IOException {
        BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
        writer.write("broadcast\n");
        writer.write(message + "\n");
        writer.flush();
    }
}

class ClientThread extends Thread {
    private Socket socket;

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

    @Override
    public void run() {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            while (true) {
                String message = reader.readLine();
                if (message == null) {
                    continue;
                }
                System.out.println(message);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

3. 工具类

import java.net.Socket;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class ServerUtils {
    private static Map<String, Socket> userSocketMap = new HashMap<>();
    private static Map<String, List<Socket>> groupSocketMap = new HashMap<>();

    // 添加用户
    public static void addUser(String username, Socket socket) {
        userSocketMap.put(username, socket);
    }

    // 获取用户socket
    public static Socket getSocket(String username) {
        return userSocketMap.get(username);
    }

    // 添加群组
    public static void addGroup(String groupName, Socket socket) {
        if (groupSocketMap.containsKey(groupName)) {
            groupSocketMap.get(groupName).add(socket);
        } else {
            List<Socket> sockets = new ArrayList<>();
            sockets.add(socket);
            groupSocketMap.put(groupName, sockets);
        }
    }

    // 获取群组socket列表
    public static List<Socket> getGroupSockets(String groupName) {
        return groupSocketMap.get(groupName);
    }

    // 获取所有socket
    public static List<Socket> getSockets() {
        List<Socket> sockets = new ArrayList<>(userSocketMap.values());
        sockets.addAll(getAllGroupSockets());
        return sockets;
    }

    // 获取所有群组socket
    private static List<Socket> getAllGroupSockets() {
        List<Socket> sockets = new ArrayList<>();
        for (List<Socket> list : groupSocketMap.values()) {
            sockets.addAll(list);
        }
        return sockets;
    }
}

以上就是基于socket的简易聊天程序的Java代码实现。其中，通过ServerUtils类实现了用户和群组的管理，ServerThread类处理客户端请求，ClientThread类接收服务端消息，Client类完成客户端的发送消息操作。此程序仅为简单示例，实际应用中需要考虑更多的异常情况和安全问题。