Java网络编程基础详解

什么是网络编程

网络编程是编写可以通过网络进行通信的应用程序。Java提供了丰富的网络编程API，支持TCP和UDP协议。

InetAddress类

InetAddress类用于表示IP地址。

import java.net.InetAddress;
import java.net.UnknownHostException;

public class InetAddressDemo {
    public static void main(String[] args) {
        try {
            InetAddress localHost = InetAddress.getLocalHost();
            System.out.println("本地主机: " + localHost);
            System.out.println("主机名: " + localHost.getHostName());
            System.out.println("IP地址: " + localHost.getHostAddress());

            InetAddress byName = InetAddress.getByName("www.baidu.com");
            System.out.println("百度IP: " + byName.getHostAddress());

            InetAddress[] allByName = InetAddress.getAllByName("www.google.com");
            for (InetAddress addr : allByName) {
                System.out.println("Google IP: " + addr.getHostAddress());
            }

            InetAddress loopback = InetAddress.getLoopbackAddress();
            System.out.println("回环地址: " + loopback);
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
    }
}

URL类

URL类用于表示统一资源定位符。

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;

public class URLDemo {
    public static void main(String[] args) {
        try {
            URL url = new URL("https://www.baidu.com");
            System.out.println("协议: " + url.getProtocol());
            System.out.println("主机: " + url.getHost());
            System.out.println("端口: " + url.getPort());
            System.out.println("路径: " + url.getPath());

            URLConnection conn = url.openConnection();
            conn.setConnectTimeout(5000);
            conn.setReadTimeout(5000);

            try (BufferedReader reader = new BufferedReader(
                    new InputStreamReader(conn.getInputStream()))) {
                String line;
                int lineCount = 0;
                while ((line = reader.readLine()) != null && lineCount < 5) {
                    System.out.println(line);
                    lineCount++;
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Socket编程

TCP Socket客户端

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

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

            out.println("Hello Server");
            String response = in.readLine();
            System.out.println("服务器响应: " + response);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

TCP Socket服务器

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

public class TcpServerDemo {
    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(8080)) {
            System.out.println("服务器启动，等待连接...");

            while (true) {
                Socket client = serverSocket.accept();
                System.out.println("客户端连接: " + client.getInetAddress());

                new Thread(() -> {
                    try (BufferedReader in = new BufferedReader(
                            new InputStreamReader(client.getInputStream()));
                         PrintWriter out = new PrintWriter(
                             client.getOutputStream(), true)) {

                        String message = in.readLine();
                        System.out.println("收到消息: " + message);
                        out.println("Echo: " + message);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

UDP Socket

UDP客户端

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class UdpClientDemo {
    public static void main(String[] args) {
        try (DatagramSocket socket = new DatagramSocket()) {
            String message = "Hello UDP Server";
            byte[] data = message.getBytes();

            InetAddress serverAddr = InetAddress.getByName("localhost");
            DatagramPacket packet = new DatagramPacket(
                data, data.length, serverAddr, 9999);

            socket.send(packet);

            byte[] buffer = new byte[1024];
            DatagramPacket response = new DatagramPacket(buffer, buffer.length);
            socket.receive(response);

            String responseMsg = new String(response.getData(), 0, response.getLength());
            System.out.println("服务器响应: " + responseMsg);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

UDP服务器

import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UdpServerDemo {
    public static void main(String[] args) {
        try (DatagramSocket socket = new DatagramSocket(9999)) {
            System.out.println("UDP服务器启动...");

            while (true) {
                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("收到消息: " + message);

                byte[] responseData = ("Echo: " + message).getBytes();
                DatagramPacket response = new DatagramPacket(
                    responseData, responseData.length,
                    packet.getAddress(), packet.getPort());
                socket.send(response);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

网络编程最佳实践

1. 设置合理的超时时间
2. 使用try-with-resources管理网络资源
3. 处理网络异常
4. 考虑使用NIO提高性能
5. 注意网络安全

总结

Java网络编程提供了丰富的API来处理网络通信。理解Socket编程和URL操作，能帮助你构建网络应用程序。