使用Java編寫Socket程序實現網路通信

一、Socket Programming是什麼

Socket Programming（套接字編程）是指使用Socket API進行網路編程。在Java中，Socket可以用來通過TCP/IP協議進行數據交換，可以實現不同機器之間的數據通信。

Socket編程通過創建Socket對象來開啟一個埠，埠號是從1到65535之間的整數。一台機器可以同時開啟多個埠，不同的埠用來提供不同的服務。

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class SocketServer {
    public static void main(String[] args) throws IOException {
        int portNumber = 8080;
        ServerSocket serverSocket = new ServerSocket(portNumber);
        while (true) {
            Socket clientSocket = serverSocket.accept();
            // 開啟線程處理客戶端請求
            new RequestHandler(clientSocket).start();
        }
    }
}

二、實現Tcp Server服務端

要實現一個Tcp Server服務端，需要創建一個ServerSocket對象，調用accept()方法等待客戶端請求，當有客戶端請求時，會返回一個Socket對象，通過該對象即可與客戶端通信。

開啟一個ServerSocket對象，設置埠號，使用accept()方法等待客戶端請求：

ServerSocket serverSocket = new ServerSocket(portNumber);
Socket clientSocket = serverSocket.accept();

獲取客戶端請求後，可以使用輸入流讀取客戶端發送的數據，使用輸出流向客戶端發送響應數據：

InputStream inputStream = clientSocket.getInputStream();
OutputStream outputStream = clientSocket.getOutputStream();

完整的Tcp Server服務端代碼示例：

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;

public class TcpServer {
    public static void main(String[] args) throws IOException {
        int portNumber = 8080;
        ServerSocket serverSocket = new ServerSocket(portNumber);
        while (true) {
            Socket clientSocket = serverSocket.accept();
            BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                out.println(inputLine);
            }
        }
    }
}

三、實現Tcp Client客戶端

要實現一個Tcp Client客戶端，需要創建一個Socket對象，連接指定的伺服器地址和埠號，然後使用輸入輸出流向伺服器發送請求和接收響應。

創建一個Socket對象，設置伺服器地址和埠號，向伺服器發送請求，並讀取響應：

Socket socket = new Socket(serverAddress, portNumber);
OutputStream outputStream = socket.getOutputStream();
InputStream inputStream = socket.getInputStream();

完整的Tcp Client客戶端代碼示例：

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

public class TcpClient {
    public static void main(String[] args) throws IOException {
        String serverAddress = "localhost";
        int portNumber = 8080;
        Socket socket = new Socket(serverAddress, portNumber);
        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
        String userInput;
        while ((userInput = stdIn.readLine()) != null) {
            out.println(userInput);
            System.out.println("echo: " + in.readLine());
        }
    }
}

四、使用UDP協議進行數據傳輸

使用UDP（User Datagram Protocol）協議可以實現不需要建立連接，直接進行數據傳輸的網路通信。相比於TCP，UDP更輕便，但無法保證數據的可靠性和順序。

使用UDP協議創建一個DatagramSocket對象，然後創建一個DatagramPacket對象，該對象包含發送或接收的數據和目標地址和埠號。通過send()方法向指定地址發送數據包，使用receive()方法接收數據包。

完整的UDP Server服務端代碼示例：

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

public class UdpServer {
    public static void main(String[] args) throws IOException {
        int portNumber = 8080;
        DatagramSocket serverSocket = new DatagramSocket(portNumber);
        byte[] receiveData = new byte[1024];
        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
        while (true) {
            serverSocket.receive(receivePacket);
            String message = new String(receivePacket.getData(), receivePacket.getOffset(), receivePacket.getLength());
            System.out.println("Received message: " + message);
            InetAddress address = receivePacket.getAddress();
            int port = receivePacket.getPort();
            byte[] sendData = message.toUpperCase().getBytes();
            DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, address, port);
            serverSocket.send(sendPacket);
        }
    }
}

完整的UDP Client客戶端代碼示例：

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

public class UdpClient {
    public static void main(String[] args) throws IOException {
        String serverAddress = "localhost";
        int portNumber = 8080;
        DatagramSocket clientSocket = new DatagramSocket();
        InetAddress address = InetAddress.getByName(serverAddress);
        byte[] sendData = "Hello, UDP!".getBytes();
        DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, address, portNumber);
        clientSocket.send(sendPacket);
        byte[] receiveData = new byte[1024];
        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
        clientSocket.receive(receivePacket);
        String message = new String(receivePacket.getData(), receivePacket.getOffset(), receivePacket.getLength());
        System.out.println("Received message: " + message);
    }
}

五、總結

本文詳細介紹了使用Java編寫Socket程序實現網路通信的方法，包括Tcp Server服務端，Tcp Client客戶端，以及UDP協議的實現方式。希望讀者能夠通過本文加深對Socket編程的理解，實踐中靈活運用。