Java Socket 基础教程

Java Socket 基础教程

Socket 简介

Socket 是网络通信的基础，允许不同主机之间进行数据传输。Java 提供了 java.net 包来实现 Socket 编程，支持 TCP 和 UDP 协议。

TCP Socket 编程

TCP 是一种面向连接的协议，提供可靠的数据传输。以下是 TCP Socket 的基本实现方式：

服务器端代码

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

public class TCPServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8080);
        System.out.println("Server started, waiting for client...");

        Socket clientSocket = serverSocket.accept();
        System.out.println("Client connected: " + clientSocket.getInetAddress());

        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);

        String message = in.readLine();
        System.out.println("Received from client: " + message);

        out.println("Hello from server");
        clientSocket.close();
        serverSocket.close();
    }
}

客户端代码

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

public class TCPClient {
    public static void main(String[] args) throws IOException {
        Socket socket = new Socket("localhost", 8080);
        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

        out.println("Hello from client");
        String response = in.readLine();
        System.out.println("Received from server: " + response);

        socket.close();
    }
}

UDP Socket 编程

UDP 是一种无连接的协议，传输速度快但不可靠。以下是 UDP Socket 的基本实现方式：

服务器端代码

import java.net.*;

public class UDPServer {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket(8080);
        byte[] buffer = new byte[1024];

        DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
        socket.receive(packet);

        String message = new String(packet.getData(), 0, packet.getLength());
        System.out.println("Received from client: " + message);

        InetAddress clientAddress = packet.getAddress();
        int clientPort = packet.getPort();
        String response = "Hello from server";
        byte[] responseData = response.getBytes();

        DatagramPacket responsePacket = new DatagramPacket(responseData, responseData.length, clientAddress, clientPort);
        socket.send(responsePacket);
        socket.close();
    }
}

客户端代码

import java.net.*;

public class UDPClient {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket();
        InetAddress serverAddress = InetAddress.getByName("localhost");

        String message = "Hello from client";
        byte[] sendData = message.getBytes();

        DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, serverAddress, 8080);
        socket.send(sendPacket);

        byte[] receiveData = new byte[1024];
        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
        socket.receive(receivePacket);

        String response = new String(receivePacket.getData(), 0, receivePacket.getLength());
        System.out.println("Received from server: " + response);

        socket.close();
    }
}

常见问题与注意事项

• 端口占用：确保端口未被其他程序占用，否则会抛出 BindException。
• 资源释放：使用完毕后关闭 Socket 和流，避免资源泄漏。
• 异常处理：网络通信可能抛出 IOException，建议使用 try-catch 块处理。
• 多线程：服务器通常需要处理多个客户端连接，可以使用多线程或线程池。

进阶学习

• NIO（非阻塞 IO）：Java 提供了 java.nio 包，支持非阻塞 IO，适合高并发场景。
• Netty 框架：基于 NIO 的高性能网络框架，简化了 Socket 编程的复杂性。