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网络编程基础：连接Java的秘密网络

article 2025/3/5 2:39:48

1 网络编程的重要性

网络编程允许Java应用程序与其他计算机或设备进行通信。这包括从简单的数据传输到复杂的分布式系统和Web服务。

2 Java网络编程的核心类

Java提供了多个类来支持网络编程：

InetAddress：表示网络上的IP地址。
URL：表示统一资源定位符，用于访问网络资源。
URLConnection：处理从URL指定的网络资源的通信。
Socket：用于TCP网络通信。
ServerSocket：等待客户端连接的服务器端Socket。
DatagramSocket：用于UDP网络通信。
DatagramPacket：包含发送或接收数据的UDP数据包。

3 创建客户端-服务器应用

Java网络编程通常涉及创建客户端和服务器应用程序，它们通过Socket进行通信。

示例代码（服务器端）：

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

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(6789);
        System.out.println("Server is listening on port 6789");

        try (Socket socket = serverSocket.accept()) {
            InputStreamReader input = new InputStreamReader(socket.getInputStream());
            BufferedReader bufRead = new BufferedReader(input);
            PrintWriter output = new PrintWriter(socket.getOutputStream(), true);

            String line;
            while ((line = bufRead.readLine()) != null) {
                System.out.println("Client: " + line);
                output.println("Server: " + line);
            }
        }
    }
}

示例代码（客户端）：

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

public class Client {
    public static void main(String[] args) throws IOException {
        Socket socket = new Socket("localhost", 6789);
        InputStreamReader input = new InputStreamReader(socket.getInputStream());
        BufferedReader bufRead = new BufferedReader(input);
        PrintWriter output = new PrintWriter(socket.getOutputStream(), true);
        BufferedReader stdInput = new BufferedReader(new InputStreamReader(System.in));

        String line;
        while ((line = stdInput.readLine()) != null) {
            output.println(line);
            System.out.println("Server: " + bufRead.readLine());
        }
    }
}

4 UDP通信

UDP是一种无连接的协议，适用于需要快速传输但不一定要求可靠到达的场景。

示例代码（UDP服务器）：

import java.net.*;

public class UDPServer {
    public static void main(String[] args) throws Exception {
        DatagramSocket serverSocket = new DatagramSocket(9876);
        byte[] receiveData = new byte[1024];
        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);

        serverSocket.receive(receivePacket);
        String sentence = new String(receivePacket.getData(), 0, receivePacket.getLength());
        System.out.println("RECEIVED: " + sentence);

        serverSocket.close();
    }
}

示例代码（UDP客户端）：

import java.net.*;

public class UDPClient {
    public static void main(String[] args) throws Exception {
        DatagramSocket clientSocket = new DatagramSocket();
        String sentence = "Hello from client";
        byte[] buf = sentence.getBytes();
        InetAddress IPAddress = InetAddress.getByName("localhost");

        DatagramPacket sendPacket = new DatagramPacket(buf, buf.length, IPAddress, 9876);
        clientSocket.send(sendPacket);
        clientSocket.close();
    }
}

5 多线程网络服务器

为了处理多个客户端，服务器通常需要使用多线程。

示例代码（多线程服务器）：

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

public class MultiThreadedServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(6789);

        while (true) {
            Socket clientSocket = serverSocket.accept();
            new ClientHandler(clientSocket).start();
        }
    }

    private static class ClientHandler extends Thread {
        private Socket clientSocket;

        public ClientHandler(Socket socket) {
            this.clientSocket = socket;
        }

        public void run() {
            try {
                InputStreamReader input = new InputStreamReader(clientSocket.getInputStream());
                BufferedReader bufRead = new BufferedReader(input);
                PrintWriter output = new PrintWriter(clientSocket.getOutputStream(), true);

                String line;
                while ((line = bufRead.readLine()) != null) {
                    System.out.println("Client: " + line);
                    output.println("Server: " + line);
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    clientSocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}