Download a file via a proxy java

Question

i have a problem downloading a file from a url like www.example.com/example.pdf via a proxy and saving it on the filesystem in java. Does anybody have an Idea on how this could work? if I get the InputStream i can simply save it to filesystem with this:

final ReadableByteChannel rbc = Channels.newChannel(httpUrlConnetion.getInputStream());    
final FileOutputStream fos = new FileOutputStream(file);
fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
fos.close();

but how to get the inputstream of the a url via a prox? if i am doing it like this:

SocketAddress addr = new InetSocketAddress("my.proxy.com", 8080);
Proxy proxy = new Proxy(Proxy.Type.HTTP, addr);
URL url = new URL("http://my.real.url.com/");
URLConnection conn = url.openConnection(proxy);

i am getting this exception:

java.net.SocketException: Connection reset
    at java.net.SocketInputStream.read(Unknown Source)
    at java.net.SocketInputStream.read(Unknown Source)
    at java.io.BufferedInputStream.fill(Unknown Source)
    at java.io.BufferedInputStream.read1(Unknown Source)
    at java.io.BufferedInputStream.read(Unknown Source)
    at sun.net.www.http.HttpClient.parseHTTPHeader(Unknown Source)
    at sun.net.www.http.HttpClient.parseHTTP(Unknown Source)
    at sun.net.www.http.HttpClient.parseHTTP(Unknown Source)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
    at app.model.mail.crawler.newimpl.FileLoader.getSourceOfSiteViaProxy(FileLoader.java:167)
    at app.model.mail.crawler.newimpl.FileLoader.process(FileLoader.java:220)
    at app.model.mail.crawler.newimpl.FileLoader.run(FileLoader.java:57)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

using this:

final HttpURLConnection httpUrlConnetion = (HttpURLConnection) website.openConnection(proxy);
httpUrlConnetion.setDoOutput(true);
httpUrlConnetion.setDoInput(true);
httpUrlConnetion.setRequestProperty("Content-type", "text/xml");
httpUrlConnetion.setRequestProperty("Accept", "text/xml, application/xml");
httpUrlConnetion.setRequestMethod("POST");
httpUrlConnetion.connect();

i am able to download the source of a site which is html, but not a file maybe someone could help me with the properties i have to set for downloading a file.

Answer 1

To set a proxy programmatically:

SocketAddress addr = new InetSocketAddress("my.proxy.com", 8080);
Proxy proxy = new Proxy(Proxy.Type.HTTP, addr);
URL url = new URL("http://my.real.url.com/");
URLConnection conn = url.openConnection(proxy);

Then you can use your code above with the URLConnection returned on the last line. You can also use a SOCKS proxy, or force no proxy, if you so desire.

This was taken (and slightly edited) from this Oracle documentation.

Answer 2

Another approach is to implement the proxy "inside" each instance of httpUrlConnection. That is:

1. Do not connect to the real URL you want. First, connect to the proxy IP and port, but with the http GET method refering to the URL you want.
2. Use the setRequestProperty to set the host to your URL's and any other header you may need.

If it works, the connection will transparently send the file to you.

I have some code that worked with Sockets.

try {
    Socket sock = new Socket("10.0.241.1", 3128); //proxy IP and port
    InputStream is = sock.getInputStream();
    OutputStream os = sock.getOutputStream();
    String str = "GET http://www.uol.com.br HTTP/1.1\r\n"; //GET your site
    str += "Host: www.uol.com.br\r\n"; //again, Host of your site
    str += "Proxy-Authorization: Basic ZWR1YXJkby5wb2NvOmM1NmQyMw==\r\n"; //if password is needed
    str += "\r\n";
    os.write(str.getBytes());
    byte[] bb = new byte[1024];
    int L = 0;
    while ((L = is.read(bb)) != -1) {
        //write bytes to file stream...
    }
} catch (Exception ex) {
    //exception handling...
}

"Why would somebody use pure sockets when one could use httpUrlConnection?", you say. Well, by that time, I didn't know about httpUrlConnection.

Answer 3

It is possible to use the library Apache httpclient that solves most of the issue with proxies. To compile the code below, you can use the following maven:

Maven:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>stackoverflow.test</groupId>
  <artifactId>proxyhttp</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>proxy</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.apache.httpcomponents</groupId>
      <artifactId>httpclient</artifactId>
      <version>4.5.1</version>
    </dependency>
  </dependencies>
</project>

Java code:

import org.apache.http.HttpHost;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

/**
 * How to send a request via proxy.
 *
 * @since 4.0
 */
public class ClientExecuteProxy {

    public static void main(String[] args)throws Exception {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            HttpHost target = new HttpHost("www.google.com", 80, "http");
            HttpHost proxy = new HttpHost("127.0.0.1", 8889, "http");

            RequestConfig config = RequestConfig.custom()
                    .setProxy(proxy)
                    .build();
            HttpGet request = new HttpGet("/");
            request.setConfig(config);

            System.out.println("Executing request " + request.getRequestLine() + " to " + target + " via " + proxy);

            CloseableHttpResponse response = httpclient.execute(target, request);
            try {
                System.out.println("----------------------------------------");
                System.out.println(response.getStatusLine());
                System.out.println(EntityUtils.toString(response.getEntity()));
            } finally {
                response.close();
            }
        } finally {
            httpclient.close();
        }
    }

}