import java.io.*;
import java.net.*;
import java.util.*;
 
// 服務器類
public class ChatServer {
    private static final int PORT = 12345;
    private static Map<String, PrintWriter> clients = new HashMap<>();
 
    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(PORT)) {
            System.out.println("Chat Server is running on port " + PORT);
            while (true) {
                new ClientHandler(serverSocket.accept()).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
    // 客戶端處理類
    private static class ClientHandler extends Thread {
        private Socket socket;
        private PrintWriter out;
        private BufferedReader in;
        private String clientName;
 
        public ClientHandler(Socket socket) {
            this.socket = socket;
        }
 
        @Override
        public void run() {
            try {
                out = new PrintWriter(socket.getOutputStream(), true);
                in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
 
                // 獲取客戶端名稱
                clientName = in.readLine();
                clients.put(clientName, out);
                System.out.println(clientName + " has joined the chat.");
 
                String inputLine;
                while ((inputLine = in.readLine()) != null) {
                    if (inputLine.startsWith("/msg")) {
                        String[] parts = inputLine.split(" ", 3);
                        if (parts.length == 3) {
                            String recipient = parts[1];
                            String message = parts[2];
                            sendPrivateMessage(clientName, recipient, message);
                        }
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    socket.close();
                    clients.remove(clientName);
                    System.out.println(clientName + " has left the chat.");
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
 
        // 發(fā)送私聊消息
        private void sendPrivateMessage(String sender, String recipient, String message) {
            PrintWriter recipientWriter = clients.get(recipient);
            if (recipientWriter != null) {
                recipientWriter.println(sender + " whispers: " + message);
            } else {
                out.println("User " + recipient + " not found.");
            }
        }
    }
} 
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import java.io.*;
import java.net.*;
import java.util.Scanner;
 
// 客戶端類
public class ChatClient {
    private static final String SERVER_ADDRESS = "localhost";
    private static final int PORT = 12345;
 
    public static void main(String[] args) {
        try (Socket socket = new Socket(SERVER_ADDRESS, PORT);
             PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
             BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
             Scanner scanner = new Scanner(System.in)) {
 
            System.out.print("Enter your name: ");
            String name = scanner.nextLine();
            out.println(name);
 
            // 啟動一個線程來接收服務器消息
            new Thread(() -> {
                try {
                    String inputLine;
                    while ((inputLine = in.readLine()) != null) {
                        System.out.println(inputLine);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }).start();
 
            // 讀取用戶輸入并發(fā)送消息
            String input;
            while (scanner.hasNextLine()) {
                input = scanner.nextLine();
                out.println(input);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}