使用Java编写Socket程序实现网络通信

一、Socket Programming是什么

Socket Programming（套接字编程）是指使用Socket API进行网络编程。在Java中，Socket可以用来通过TCP/IP协议进行数据交换，可以实现不同机器之间的数据通信。

Socket编程通过创建Socket对象来开启一个端口，端口号是从1到65535之间的整数。一台机器可以同时开启多个端口，不同的端口用来提供不同的服务。

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();
            // 开启线程处理客户端请求
            new RequestHandler(clientSocket).start();
        }
    }
}

二、实现Tcp Server服务端

要实现一个Tcp Server服务端，需要创建一个ServerSocket对象，调用accept()方法等待客户端请求，当有客户端请求时，会返回一个Socket对象，通过该对象即可与客户端通信。

开启一个ServerSocket对象，设置端口号，使用accept()方法等待客户端请求：

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

获取客户端请求后，可以使用输入流读取客户端发送的数据，使用输出流向客户端发送响应数据：

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

完整的Tcp Server服务端代码示例：

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、实现Tcp Client客户端

要实现一个Tcp Client客户端，需要创建一个Socket对象，连接指定的服务器地址和端口号，然后使用输入输出流向服务器发送请求和接收响应。

创建一个Socket对象，设置服务器地址和端口号，向服务器发送请求，并读取响应：

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

完整的Tcp Client客户端代码示例：

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协议进行数据传输

使用UDP（User Datagram Protocol）协议可以实现不需要建立连接，直接进行数据传输的网络通信。相比于TCP，UDP更轻便，但无法保证数据的可靠性和顺序。

使用UDP协议创建一个DatagramSocket对象，然后创建一个DatagramPacket对象，该对象包含发送或接收的数据和目标地址和端口号。通过send()方法向指定地址发送数据包，使用receive()方法接收数据包。

完整的UDP Server服务端代码示例：

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客户端代码示例：

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、总结

本文详细介绍了使用Java编写Socket程序实现网络通信的方法，包括Tcp Server服务端，Tcp Client客户端，以及UDP协议的实现方式。希望读者能够通过本文加深对Socket编程的理解，实践中灵活运用。