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 概述

实现一个UDP代理服务器，它监听一个指定的端口，将接收到的UDP数据包转发到目标主机，并将目标主机的响应转发回原始客户端。使用线程池来异步处理响应，并使用日志记录器来记录不同级别的日志信息。

源代码

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.nio.charset.StandardCharsets;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;public class UDPProxy {private final int listenPort;private final String targetHost;private final int targetPort;private final Map<DatagramSocket, DatagramPacket> downPacketCache = new ConcurrentHashMap<>();private final ThreadPoolExecutor executor = new ThreadPoolExecutor(8, 16,60L, TimeUnit.SECONDS, new LinkedBlockingQueue<>(200), new ThreadPoolExecutor.CallerRunsPolicy());private static final Logger logger = Logger.getLogger("UDPProxy");public UDPProxy(int listenPort, String targetHost, int targetPort) {this.listenPort = listenPort;this.targetHost = targetHost;this.targetPort = targetPort;//设置日志级别logger.setLevel(Level.INFO);}public void start() {try (DatagramSocket thisSocket = new DatagramSocket(listenPort)) {byte[] receiveData = new byte[4096];logger.warning("UDP Proxy started, listening on port " + listenPort);Map<InetAddress, DatagramSocket> upSocketCache = new ConcurrentHashMap<>();while (true) {DatagramPacket upPacket = new DatagramPacket(receiveData, receiveData.length);thisSocket.receive(upPacket);byte[] data = upPacket.getData();int length = upPacket.getLength();InetAddress clientAddress = upPacket.getAddress();logger.warning("[UP] Size:" + length + ",from" + clientAddress + ":" + upPacket.getPort());logger.info("[UP] Packet:" + new String(data, 0, length, StandardCharsets.UTF_8));// Forward the packet to the target hostInetAddress targetAddress = InetAddress.getByName(targetHost);DatagramPacket sendPacket = new DatagramPacket(data, length, targetAddress, targetPort);DatagramSocket upSocket = upSocketCache.get(clientAddress);if (upSocket == null) {upSocket = new DatagramSocket();upSocketCache.put(clientAddress, upSocket);downPacketCache.put(upSocket, upPacket);upSocket.send(sendPacket);responseListener(thisSocket, upSocket);} else {upSocket.send(sendPacket);}}} catch (IOException e) {logger.log(Level.SEVERE, "Error in UDPProxy", e);}}private void responseListener(DatagramSocket thisSocket, DatagramSocket upSocket) {executor.execute(() -> {while (true) {byte[] downData = new byte[4096];DatagramPacket downPacket = new DatagramPacket(downData, downData.length);byte[] data = downPacket.getData();InetAddress downPacketAddress;try {upSocket.receive(downPacket);downPacketAddress = downPacket.getAddress();int length = downPacket.getLength();logger.warning("[DOWN] Size:" + length + ",From" + downPacketAddress + ":" + downPacket.getPort());logger.info("[DOWN] Packet:"+ new String(data, 0, length, StandardCharsets.UTF_8));DatagramPacket datagramPacket = downPacketCache.get(upSocket);if (datagramPacket != null) {datagramPacket.setData(data);thisSocket.send(datagramPacket);}} catch (IOException e) {logger.log(Level.SEVERE, "Error in responseListener", e);}}});}public static void main(String[] args) {if (args.length != 3) {logger.warning("Usage: java UDPProxy <listenPort> <targetHost> <targetPort>");System.exit(1);}int listenPort = Integer.parseInt(args[0]);String targetHost = args[1];int targetPort = Integer.parseInt(args[2]);UDPProxy proxy = new UDPProxy(listenPort, targetHost, targetPort);proxy.start();}
}

代码启动

java UDPProxy <listenPort> <targetHost> <targetPort>

• listenPort：代理服务器监听的端口。

• targetHost：目标主机的地址。

• targetPort：目标主机的端口。

 java UDPProxy 12681 192.168.18.76 6666

代码剖析

类和成员变量

1. 成员变量：

   • listenPort：代理服务器监听的端口。

   • targetHost：目标主机的地址。

   • targetPort：目标主机的端口。

   • downPacketCache：用于缓存下行数据包的映射。

   • executor：用于处理响应监听的线程池。

   • logger：用于日志记录的Logger对象。

构造方法

• 构造方法：

  • 初始化listenPort、targetHost和targetPort。

  • 设置日志级别为INFO。

start方法

• start方法：

  • 创建一个DatagramSocket实例，监听指定的端口。

  • 无限循环接收传入的UDP数据包。

  • 将接收到的数据包转发到目标主机。

  • 使用upSocketCache缓存每个客户端的DatagramSocket实例。

  • 调用responseListener方法监听目标主机的响应。

responseListener方法

• responseListener方法：

  • 使用线程池异步处理目标主机的响应。

  • 接收目标主机的响应数据包。

  • 从downPacketCache中获取原始客户端的数据包，并将响应数据包发送回原始客户端。

main方法

• main方法：

  • 解析命令行参数，创建UDPProxy实例并启动代理服务器。