用java写一个socks5代理

可以使用Java Socket类来实现一个简单的Socks5代理。以下是一个示例代码：

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class Socks5Proxy {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(1080);
        System.out.println("Socks5 proxy started on port 1080");

        while (true) {
            Socket clientSocket = serverSocket.accept();
            System.out.println("Accepted connection from " + clientSocket.getInetAddress());

            new Thread(() -> {
                try {
                    InputStream clientIn = clientSocket.getInputStream();
                    OutputStream clientOut = clientSocket.getOutputStream();

                    // Read the Socks5 handshake request
                    byte[] buf = new byte[1024];
                    int len = clientIn.read(buf);
                    if (buf[0] != 0x05) {
                        throw new IOException("Invalid Socks5 handshake request");
                    }

                    // Send the Socks5 handshake response
                    clientOut.write(new byte[] { 0x05, 0x00 });

                    // Read the Socks5 request
                    len = clientIn.read(buf);
                    if (buf[0] != 0x05 || buf[1] != 0x01 || buf[2] != 0x00) {
                        throw new IOException("Invalid Socks5 request");
                    }

                    // Parse the Socks5 request
                    int port = ((buf[len - 2] & 0xff) << 8) | (buf[len - 1] & 0xff);
                    String host = null;
                    switch (buf[3]) {
                        case 0x01:
                            host = String.format("%d.%d.%d.%d", buf[4], buf[5], buf[6], buf[7]);
                            break;
                        case 0x03:
                            int hostLen = buf[4];
                            host = new String(buf, 5, hostLen);
                            break;
                        case 0x04:
                            host = String.format("[%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x]",
                                    buf[4], buf[5], buf[6], buf[7], buf[8], buf[9], buf[10], buf[11],
                                    buf[12], buf[13], buf[14], buf[15], buf[16], buf[17], buf[18], buf[19]);
                            break;
                        default:
                            throw new IOException("Invalid Socks5 request");
                    }

                    System.out.println("Connecting to " + host + ":" + port);

                    // Connect to the destination server
                    Socket serverSocket = new Socket(host, port);
                    InputStream serverIn = serverSocket.getInputStream();
                    OutputStream serverOut = serverSocket.getOutputStream();

                    // Send the Socks5 response
                    byte[] response = new byte[len];
                    System.arraycopy(buf, 0, response, 0, len);
                    response[1] = 0x00;
                    clientOut.write(response);

                    // Start forwarding data between client and server
                    new Thread(() -> {
                        try {
                            byte[] buf2 = new byte[1024];
                            int len2;
                            while ((len2 = serverIn.read(buf2)) != -1) {
                                clientOut.write(buf2, 0, len2);
                            }
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }).start();

                    byte[] buf3 = new byte[1024];
                    int len3;
                    while ((len3 = clientIn.read(buf3)) != -1) {
                        serverOut.write(buf3, 0, len3);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }).start();
        }
    }
}

这个代理服务器监听1080端口，当有客户端连接时，它会读取Socks5握手请求，然后发送Socks5握手响应。接下来，它会读取Socks5请求，解析出目标主机和端口，然后连接到目标服务器。一旦连接建立，它会发送Socks5响应，然后开始转发数据。