Java 中的简单 Web 代理

Question

我正在尝试用java编写一个简单的Web代理，它接受GET和POST请求。我写了以下代码：

import java.net.*;
import java.io.*;
import java.nio.CharBuffer;
import java.util.logging.Level;
import java.util.logging.Logger;
public class InterceptionProxy2 {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;
        boolean listening = true;
        int port = 1234;
        try {
            serverSocket = new ServerSocket(port);
        } catch (IOException e) {
            System.out.println("Port Error");
            System.exit(-1);
        }
        while (listening) {
            new ProxyThread2(serverSocket.accept()).start();
        }
        serverSocket.close();
    }
}
class ProxyThread2 extends Thread {
    private Socket clientSocket = null;
    private Socket serverSocket = null;
    public ProxyThread2(Socket socket) {
        super("ProxyThread2");
        this.clientSocket = socket;
    }
    public void run() {
        //Stream to put data to the browser
        PrintWriter outGoing = null;
        try {
            outGoing = new PrintWriter(clientSocket.getOutputStream(), true);
            //Stream to get data from the browser
            BufferedReader inComing = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            String incomingRequest;
            String url = "";
            String request = "";
            String response = "";
            //Take the incoming request
            char[] buf = new char[8196];        //8196 is the default max size for GET requests in Apache
            int bytesRead = inComing.read(buf);   //BytesRead need to be calculated if the char buffer contains too many values
            request = new String(buf, 0, bytesRead);
            System.out.println("Request");
            System.out.println(request);
            //Create a new socket for connecting to destination server
            serverSocket = new Socket("localhost", 80);
            PrintWriter pOut = new PrintWriter(serverSocket.getOutputStream(), true);
            //Reader for response from destination server
            BufferedReader pIn = new BufferedReader(new InputStreamReader(serverSocket.getInputStream()));
            //Put data into the new socket(to the apache server) and receive its output
            pOut.print(request);
            pOut.flush();
            bytesRead = pIn.read(buf);
            //Check if data is read
            if (bytesRead > 0) {
                response = new String(buf, 0, bytesRead);
            }
            System.out.println("Response");
            System.out.println(response);
            //Put data back into the original client socket
            outGoing.write(response);
        } catch (IOException ex) {
            Logger.getLogger(ProxyThread2.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            outGoing.close();
        }
    }
}

系统正确地将请求和响应打印为输出，但代理不会向浏览器提供回复。传出流定义有什么问题吗？还是应该创建一个新的套接字将数据发送回浏览器？

Answer 1

您不需要创建java.net.ServerSocket的另一个实例。因为您必须连接到端口 80 ，所以您是客户端。

Socket socket = new Socket("localhost", 80);

例如：

class ProxyThread extends Thread {
    private final Socket clientSocket;
    public ProxyThread(Socket socket) {
        this.clientSocket = socket;
    }
    public void run() {
        try {
            // Read request
            InputStream incommingIS = clientSocket.getInputStream();
            byte[] b = new byte[8196];
            int len = incommingIS.read(b);
            if (len > 0) {
                System.out.println("REQUEST"
                        + System.getProperty("line.separator") + "-------");
                System.out.println(new String(b, 0, len));
                // Write request
                Socket socket = new Socket("localhost", 80);
                OutputStream outgoingOS = socket.getOutputStream();
                outgoingOS.write(b, 0, len);
                // Copy response
                OutputStream incommingOS = clientSocket.getOutputStream();
                InputStream outgoingIS = socket.getInputStream();
                for (int length; (length = outgoingIS.read(b)) != -1;) {
                    incommingOS.write(b, 0, length);
                }
                incommingOS.close();
                outgoingIS.close();
                outgoingOS.close();
                incommingIS.close();
                socket.close();
            } else {
                incommingIS.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                clientSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Answer 2

适用于简单文本文件或 html 的代码。只有一个问题，只有HTTP标头是文本数据，HTTP消息正文中的所有内容都可以是简单的字节数据，如图像。

您不应该使用 PrintWriter 和/或字符串来转换响应。您应该简单地转发将从服务器获得的字节缓冲区。仅当您想向自己显示 HTTP 消息时，才转换字节缓冲区。