Java学习指南-第十一天：网络编程

　　1.网络编程简介

　　网络编程是指编写程序使计算机能够通过网络进行通信。Java提供了丰富的API来支持网络编程，主要包括java.net包中的类。

　　2.TCP/IP协议

　　TCP/IP协议是互联网的基础协议，Java中的网络编程主要基于TCP/IP协议。TCP/IP协议分为四层：

• 应用层：如HTTP、FTP等。
• 传输层：如TCP、UDP等。
• 网络层：如IP。
• 链路层：如以太网。

　　3.Socket编程

　　Socket是网络编程的基础，用于实现两台计算机之间的通信。Java中的Socket类用于客户端，ServerSocket类用于服务器端。

　　3.1服务器端

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

public class Server {
    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(12345)) {
            System.out.println("Server is listening on port 12345...");

            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("New client connected");

                new ServerThread(socket).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class ServerThread extends Thread {
    private Socket socket;

    public ServerThread(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        try (InputStream input = socket.getInputStream();
             BufferedReader reader = new BufferedReader(new InputStreamReader(input));
             OutputStream output = socket.getOutputStream();
             PrintWriter writer = new PrintWriter(output, true)) {

            String text;
            while ((text = reader.readLine()) != null) {
                System.out.println("Received: " + text);
                writer.println("Echo: " + text);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

　　3.2客户端

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

public class Client {
    public static void main(String[] args) {
        try (Socket socket = new Socket("localhost", 12345)) {
            OutputStream output = socket.getOutputStream();
            PrintWriter writer = new PrintWriter(output, true);

            InputStream input = socket.getInputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(input));

            BufferedReader consoleReader = new BufferedReader(new InputStreamReader(System.in));

            String text;
            while ((text = consoleReader.readLine()) != null) {
                writer.println(text);
                String response = reader.readLine();
                System.out.println(response);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

　　4.UDP编程

　　UDP是一种无连接的协议，数据传输速度快，但不保证数据的可靠性。Java中的DatagramSocket类用于UDP通信。

　　4.1服务器端

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

public class UDPServer {
    public static void main(String[] args) {
        try (DatagramSocket socket = new DatagramSocket(12345)) {
            System.out.println("UDP Server is listening on port 12345...");

            byte[] buffer = new byte[1024];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

            while (true) {
                socket.receive(packet);
                String received = new String(packet.getData(), 0, packet.getLength());
                System.out.println("Received: " + received);

                String response = "Echo: " + received;
                byte[] responseBytes = response.getBytes();
                DatagramPacket responsePacket = new DatagramPacket(responseBytes, responseBytes.length, packet.getAddress(), packet.getPort());
                socket.send(responsePacket);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

　　4.2客户端

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

public class UDPClient {
    public static void main(String[] args) {
        try (DatagramSocket socket = new DatagramSocket()) {
            InetAddress serverAddress = InetAddress.getByName("localhost");
            Scanner scanner = new Scanner(System.in);

            while (true) {
                System.out.print("Enter message: ");
                String message = scanner.nextLine();
                byte[] buffer = message.getBytes();
                DatagramPacket packet = new DatagramPacket(buffer, buffer.length, serverAddress, 12345);
                socket.send(packet);

                byte[] responseBuffer = new byte[1024];
                DatagramPacket responsePacket = new DatagramPacket(responseBuffer, responseBuffer.length);
                socket.receive(responsePacket);
                String response = new String(responsePacket.getData(), 0, responsePacket.getLength());
                System.out.println("Response: " + response);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

　　5.URL编程

　　Java中的URL类用于处理URL地址，可以用于读取网络资源。

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

public class URLReader {
    public static void main(String[] args) {
        try {
            URL url = new URL("https://www.example.com");
            BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
            reader.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

// TCP服务器和客户端代码见3.1和3.2

// UDP服务器和客户端代码见4.1和4.2

// URL读取代码见5.1

　　8.总结

　　今天的内容涵盖了Java网络编程的基本概念和常用技术，包括Socket编程、UDP编程和URL编程。网络编程是Java编程中非常重要的一部分，务必熟练掌握。明天我们将深入学习Java的数据库编程。

　　提示：多动手编写代码，尝试使用不同的网络编程技术解决实际问题，理解网络编程的工作原理和适用场景。

　　祝你学习愉快！