使用HttpURLConnection在发布请求上出现错误403

Question

我编写了以下代码来自动从youtube下载视频......

但我卡在中间并从服务器获得ERROR 403！

我打算做的是将带有一些参数的链接发布到服务器，然后从响应中提取下载链接，然后直接下载文件....

有什么不对？有人可以帮帮我吗？

import java.net.*;
import java.io.*;
import java.util.*;
import java.nio.charset.*;


public class Downloader{

public static void main(String[] args){

    try{

        String downloadLink = "https://www.youtube.com/watch?v=cRvl8zqAt_E&index=121&list=PL9394655A98259F67";


        URL url = new URL("http://convert2mp3.net/en/index.php");
        String addr = "127.0.0.1";
        int port = 1180;


        Map<String,Object> params = new LinkedHashMap<>();
        params.put("url", downloadLink);
        params.put("format", "mp4");
        params.put("quality", "720");


        StringBuilder postData = new StringBuilder();
        for (Map.Entry<String,Object> param : params.entrySet()) {
            if (postData.length() != 0)
                postData.append('&');
            postData.append(URLEncoder.encode(param.getKey(), "UTF-8"));
            postData.append('=');
            postData.append(URLEncoder.encode(String.valueOf(param.getValue()), "UTF-8"));
        }


        byte[] postDataBytes = postData.toString().getBytes("UTF-8");


        // I have to use proxy i.e. my ISP blocks youtube!
        Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(addr , port));
        HttpURLConnection connection = (HttpURLConnection)url.openConnection(proxy);


        connection.setRequestMethod("POST");
        connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
        connection.setRequestProperty("Content-Length", String.valueOf(postDataBytes.length));
        connection.setDoOutput(true);
        connection.getOutputStream().write(postDataBytes);

        Reader in = new BufferedReader(new InputStreamReader(connection.getInputStream(), "UTF-8"));

        for (int c; (c = in.read()) >= 0;)
            System.out.print((char)c);

    }catch(Exception ex){
        ex.printStackTrace();
    }
}
}