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

public class TcpServer {
    public static void main(String[] args) {
        try {
            // 创建ServerSocket，监听指定端口
            ServerSocket serverSocket = new ServerSocket(8080);
            System.out.println("Server started, waiting for connection...");

            // 等待客户端连接
            Socket socket = serverSocket.accept();
            System.out.println("Client connected: " + socket.getInetAddress().getHostAddress());

            // 获取输入流，读取客户端发送的数据
            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String message = reader.readLine();
            System.out.println("Received from client: " + message);

            // 获取输出流，向客户端发送数据
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
            writer.println("Hello, Client! I received your message: " + message);

            // 关闭资源
            reader.close();
            writer.close();
            socket.close();
            serverSocket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

客户端实现

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

public class TcpClient {
    public static void main(String[] args) {
        try {
            // 创建Socket，连接到服务器
            Socket socket = new Socket("localhost", 8080);
            System.out.println("Connected to server");

            // 获取输出流，向服务器发送数据
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
            writer.println("Hello, Server!");

            // 获取输入流，读取服务器发送的数据
            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String message = reader.readLine();
            System.out.println("Received from server: " + message);

            // 关闭资源
            writer.close();
            reader.close();
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

多线程TCP服务器

单线程TCP服务器只能处理一个客户端连接，多线程TCP服务器可以同时处理多个客户端连接。

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

public class MultiThreadTcpServer {
    public static void main(String[] args) {
        try {
            ServerSocket serverSocket = new ServerSocket(8080);
            System.out.println("Multi-thread server started, waiting for connections...");

            while (true) {
                // 等待客户端连接
                Socket socket = serverSocket.accept();
                System.out.println("Client connected: " + socket.getInetAddress().getHostAddress());

                // 创建新线程处理客户端连接
                new ClientHandler(socket).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 客户端处理器
    private static class ClientHandler extends Thread {
        private Socket socket;

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

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

                String message;
                while ((message = reader.readLine()) != null) {
                    System.out.println("Received from client " + socket.getInetAddress().getHostAddress() + ": " + message);
                    writer.println("Server received: " + message);
                }

                reader.close();
                writer.close();
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

UDP编程

UDP(用户数据报协议)是一种无连接的、不可靠的通信协议，不保证数据的有序传输和完整性，但传输效率高。

UDP编程的基本模型

UDP编程不需要建立连接，直接发送数据报：

发送方：创建DatagramSocket，封装数据为DatagramPacket，发送数据。
接收方：创建DatagramSocket，绑定端口，接收DatagramPacket，解析数据。

发送方实现

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

public class UdpSender {
    public static void main(String[] args) {
        try {
            // 创建DatagramSocket
            DatagramSocket socket = new DatagramSocket();

            // 准备数据
            String message = "Hello, UDP Receiver!";
            byte[] data = message.getBytes();

            // 创建DatagramPacket，指定数据、长度、接收方IP和端口
            InetAddress address = InetAddress.getByName("localhost");
            int port = 8080;
            DatagramPacket packet = new DatagramPacket(data, data.length, address, port);

            // 发送数据
            socket.send(packet);
            System.out.println("Message sent: " + message);

            // 关闭资源
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

接收方实现

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

public class UdpReceiver {
    public static void main(String[] args) {
        try {
            // 创建DatagramSocket，绑定端口
            DatagramSocket socket = new DatagramSocket(8080);
            System.out.println("Receiver started, waiting for message...");

            // 创建DatagramPacket，用于接收数据
            byte[] buffer = new byte[1024];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

            // 接收数据
            socket.receive(packet);

            // 解析数据
            String message = new String(packet.getData(), 0, packet.getLength());
            System.out.println("Received from " + packet.getAddress().getHostAddress() + ": " + message);

            // 关闭资源
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

HTTP编程

HTTP(超文本传输协议)是一种基于TCP的应用层协议，用于Web通信。Java提供了HttpURLConnection类来实现HTTP编程。

HTTP请求

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

public class HttpGetRequest {
    public static void main(String[] args) {
        try {
            // 创建URL对象
            URL url = new URL("https://www.example.com");

            // 打开连接
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();

            // 设置请求方法
            connection.setRequestMethod("GET");

            // 设置请求头
            connection.setRequestProperty("User-Agent", "Mozilla/5.0");

            // 获取响应码
            int responseCode = connection.getResponseCode();
            System.out.println("Response Code: " + responseCode);

            // 读取响应内容
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String line;
            StringBuilder response = new StringBuilder();
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
            reader.close();

            System.out.println("Response Content: " + response.toString());

            // 关闭连接
            connection.disconnect();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

HTTP POST请求

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

public class HttpPostRequest {
    public static void main(String[] args) {
        try {
            // 创建URL对象
            URL url = new URL("https://www.example.com/api");

            // 打开连接
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();

            // 设置请求方法
            connection.setRequestMethod("POST");

            // 设置请求头
            connection.setRequestProperty("Content-Type", "application/json");
            connection.setRequestProperty("User-Agent", "Mozilla/5.0");

            // 允许输出
            connection.setDoOutput(true);

            // 准备请求体
            String requestBody = "{\"name\": \"John\", \"age\": 25}";

            // 写入请求体
            OutputStream os = connection.getOutputStream();
            os.write(requestBody.getBytes());
            os.flush();
            os.close();

            // 获取响应码
            int responseCode = connection.getResponseCode();
            System.out.println("Response Code: " + responseCode);

            // 读取响应内容
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String line;
            StringBuilder response = new StringBuilder();
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
            reader.close();

            System.out.println("Response Content: " + response.toString());

            // 关闭连接
            connection.disconnect();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

URL和URLConnection

URL类用于表示统一资源定位符，URLConnection类用于建立与URL的连接。

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

public class UrlDemo {
    public static void main(String[] args) {
        try {
            // 创建URL对象
            URL url = new URL("https://www.example.com");

            // 获取URL的各个部分
            System.out.println("Protocol: " + url.getProtocol());
            System.out.println("Host: " + url.getHost());
            System.out.println("Port: " + url.getPort());
            System.out.println("Path: " + url.getPath());
            System.out.println("Query: " + url.getQuery());

            // 打开连接
            URLConnection connection = url.openConnection();

            // 获取连接属性
            System.out.println("Content-Type: " + connection.getContentType());
            System.out.println("Content-Length: " + connection.getContentLength());
            System.out.println("Last-Modified: " + connection.getLastModified());

            // 读取内容
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

网络编程的最佳实践

异常处理

网络编程容易出现各种异常，如连接失败、超时等，应正确处理异常。

资源关闭

使用完网络资源后应及时关闭，避免资源泄露。

超时设置

设置合理的超时时间，避免程序长时间等待。

// 设置连接超时时间
connection.setConnectTimeout(5000);  // 5秒

// 设置读取超时时间
connection.setReadTimeout(5000);  // 5秒

线程池的使用

在处理多个客户端连接时，使用线程池可以提高性能和资源利用率。

// 创建线程池
ExecutorService executor = Executors.newFixedThreadPool(10);

// 处理客户端连接
executor.submit(new ClientHandler(socket));

// 关闭线程池
executor.shutdown();