Setting JVM/JRE to use Windows Proxy Automatically

Question

Hey everyone,

I did see the question about setting the proxy for the JVM but what I want to ask is how one can utilize the proxy that is already configured (on Windows).

Here is a demonstration of my issue:

1. Go to your Control Panel->Java and set a proxy address.
2. Run the following simple applet code (I'm using the Eclipse IDE):

import java.awt.Graphics;
import javax.swing.JApplet;
import java.util.*;

public class Stacklet extends JApplet {
    private String message;
    public void init(){
     Properties props = System.getProperties();
     message = props.getProperty("http.proxyHost", "NONE");  
     message = (message.length() == 0)? "NONE": message;
    }

    public void paint(Graphics g)
    {
     g.drawString(message, 20, 20);
    }
}

The Applet displays "NONE" without regard to the settings you've placed in the Java Control Panel. What would be best would be if the Windows proxy settings (usually set in Internet Explorer) were what I could determine but doing an extra configuration step in the Java Control Panel would still be an acceptable solution.

Thanks!

Answer 1

It is possible to detect the proxy using the ProxySelector class and assign the system proxy by assigning environment variables with the setProperty method of the System class:

System.setProperty("java.net.useSystemProxies", "true");
System.out.println("detecting proxies");
List l = null;
try {
    l = ProxySelector.getDefault().select(new URI("http://foo/bar"));
} 
catch (URISyntaxException e) {
    e.printStackTrace();
}
if (l != null) {
    for (Iterator iter = l.iterator(); iter.hasNext();) {
     java.net.Proxy proxy = (java.net.Proxy) iter.next();
     System.out.println("proxy hostname : " + proxy.type());

     InetSocketAddress addr = (InetSocketAddress) proxy.address();

     if (addr == null) {
      System.out.println("No Proxy");
     } else {
      System.out.println("proxy hostname : " + addr.getHostName());
      System.setProperty("http.proxyHost", addr.getHostName());
      System.out.println("proxy port : " + addr.getPort());
      System.setProperty("http.proxyPort", Integer.toString(addr.getPort()));
     }
    }
}

Answer 2

If you use java.net.URL.openStream() to get an InputStream for the web resource content you automatically get the same proxy used as Internet Explorer would use for that URL.

No need to go to the Java Control Panel or to display the proxy used.