Java Socket 雙向通訊實現：基於 java.net 標準 API 的客戶端/服務端模板

阻塞式 Socket 通訊標準流程

僅依賴 JDK java.net 標準庫，無需第三方框架，適合輕量級、特定協議的通訊場景。

服務端實現模板

public class TcpServer {
    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(0)) { // 0 = 自動分配端口
            System.out.println("Server listen on: " + serverSocket.getLocalPort());
            boolean running = true;
            while (running) {
                try (Socket clientSocket = serverSocket.accept();
                     DataInputStream in = new DataInputStream(
                         new BufferedInputStream(clientSocket.getInputStream()));
                     PrintStream out = new PrintStream(
                         new BufferedOutputStream(clientSocket.getOutputStream()))) {

                    // === 業務處理邏輯 ===
                    String request = in.readUTF();
                    String response = processRequest(request);
                    out.println(response);
                    out.flush();

                } catch (IOException e) {
                    System.err.println("Client handling error: " + e.getMessage());
                }
            }
        } catch (IOException e) {
            System.err.println("Server fatal: " + e.getMessage());
        }
    }

    private static String processRequest(String req) {
        // 實際業務邏輯
        return "ECHO: " + req;
    }
}

客戶端實現模板

public class TcpClient {
    public static void main(String[] args) {
        String host = "localhost";
        int port = 12345; // 需與服務端一致

        try (Socket socket = new Socket(host, port);
             DataInputStream in = new DataInputStream(socket.getInputStream());
             PrintStream out = new PrintStream(socket.getOutputStream())) {

            out.println("Hello Server");
            out.flush();

            String response = in.readUTF();
            System.out.println("Server reply: " + response);

        } catch (IOException e) {
            System.err.println("Client error: " + e.getMessage());
        }
    }
}

關鍵技術要點

擴展方向：從單線程到高併發

• 線程池模型：ExecutorService 接收任務，每連接一線程 (適合連接數 < 500)
• NIO 非阻塞：Selector + ServerSocketChannel 單線程管理萬級連接 (Netty/Mina 封裝)
• 應用層協議：定義消息頭(長度/類型) + 體，解決 TCP 粘包/半包
• 心跳與重連：客戶端定時 PING，斷線指數退避重連

選型建議：教學/原型/極簡場景用原生 Socket；生產系統直接上 Netty/gRPC，專注業務而非通訊基建。