Java Network How to - Add Proxy server and handle Proxy Authenticator to URL connection

Question

We would like to know how to add Proxy server and handle Proxy Authenticator to URL connection.
Answer

import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.Authenticator;
import java.net.HttpURLConnection;
import java.net.InetSocketAddress;
import java.net.PasswordAuthentication;
import java.net.Proxy;
import java.net.SocketAddress;
import java.net.URL;
//from  w  ww  . j av  a2s. c o m
class ProxyAuthenticator extends Authenticator {

  private String userName, password;

  public ProxyAuthenticator(String userName, String password) {
    this.userName = userName;
    this.password = password;
  }

  protected PasswordAuthentication getPasswordAuthentication() {
    return new PasswordAuthentication(userName, password.toCharArray());
  }
}

public class Main {
  public static void main(String[] args) throws Exception {
    downloadFromUrl("http://www.java2s.com/style/download.png");
  }

  private static String getOutputFileName(URL url) {
    String[] urlParts = url.getPath().split("/");
    return "c:/temp/" + urlParts[urlParts.length - 1];
  }

  private static void downloadFromUrl(String urlString) throws Exception {
    InputStream is = null;
    FileOutputStream fos = null;

    URL url = new URL(urlString);

    System.out.println("Reading..." + url);

    Authenticator.setDefault(new ProxyAuthenticator("username", "password"));

    SocketAddress addr = new InetSocketAddress("your proxyserver ip address", 80);
    Proxy proxy = new Proxy(Proxy.Type.HTTP, addr);

    HttpURLConnection conn = (HttpURLConnection) url.openConnection(proxy);

    is = conn.getInputStream();

    String filename = getOutputFileName(url);

    fos = new FileOutputStream(filename);

    byte[] readData = new byte[1024];

    int i = is.read(readData);

    while (i != -1) {
      fos.write(readData, 0, i);
      i = is.read(readData);
    }

    System.out.println("Created file: " + filename);
    System.out.println("Completed");
  }
}