Socket 通信實戰：基於 DOS 命令行的私聊/群聊雙模式實現

架構設計

• Server：單線程接受連接，為每客戶端啟動線程，維護 Vector<Socket> 在線列表
• Client：雙線程模型（ClientSend 發送 / ClientReceive 接收）
• 協議約定：@IP:PORT 內容 為私聊，其餘為群聊

服務端核心邏輯

public class Server extends Thread {
    private static Vector<Socket> clients = new Vector<>();
    private Socket clientSocket;
    private BufferedReader in;
    private PrintWriter out;

    public static void main(String[] args) throws IOException {
        ServerSocket server = new ServerSocket(2014);
        System.out.println("服務器啟動！");
        while (true) {
            new Server(server.accept()).start();
        }
    }

    public Server(Socket socket) {
        this.clientSocket = socket;
        clients.add(socket);
        // 初始化流...
    }

    @Override
    public void run() {
        try {
            welcomeNewClient();  // 歡迎語 + 廣播上線通知
            while (true) {
                String msg = in.readLine();
                if ("bye".equals(msg) || "拜拜".equals(msg)) {
                    offline(); break;
                } else if (msg.startsWith("@") && msg.indexOf(' ') > 0) {
                    privateChat(msg);  // @IP:PORT 內容
                } else {
                    broadcast(msg);    // 群聊
                }
            }
        } catch (IOException e) { /* 忽略 */ }
    }

    private void privateChat(String msg) {
        int end = msg.indexOf(' ');
        String targetAddr = msg.substring(1, end);
        for (Socket s : clients) {
            String addr = s.getInetAddress().toString().replace("/", "") + ":" + s.getPort();
            if (targetAddr.equals(addr)) {
                String sender = clientSocket.getInetAddress().toString().replace("/", "") 
                              + ":" + clientSocket.getPort();
                new PrintWriter(s.getOutputStream(), true)
                    .println("大神" + sender + " 對你 說: " + msg.substring(end));
                break;
            }
        }
    }
    // broadcast(), welcomeNewClient(), offline() 類似...
}

客戶端雙線程模型

// 發送線程
class ClientSend extends Thread {
    private PrintWriter out;
    public void run() {
        Scanner sc = new Scanner(System.in);
        String msg = sc.nextLine();
        while (true) {
            if ("bye".equals(msg) || "拜拜".equals(msg)) { out.println(msg); break; }
            out.println(msg);
            msg = sc.nextLine();
        }
    }
}

// 接收線程
class ClientReceive extends Thread {
    private BufferedReader in;
    public void run() {
        try {
            String msg = in.readLine();
            while (!"bye".equals(msg)) {
                System.out.println(msg);
                msg = in.readLine();
            }
        } catch (IOException e) { e.printStackTrace(); }
    }
}

運行測試

1. 啟動 Server
2. 多個終端啟動 Client
3. 群聊：直接輸入文字
4. 私聊：@127.0.0.1:12345 你好（@ 後必須有空格）

代碼亮點與不足

完整代碼見：GitHub 項目