Setting JVM/JRE to use Windows Proxy Automatically

Question

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:

Go to your Control Panel->Java and set a proxy address.

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!

xav · Accepted Answer · 2015-03-03 08:58:14Z

39

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 type: " + 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()));
        }
    }
}

edited Mar 3, 2015 at 8:58

xav

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answered Dec 19, 2008 at 17:58

t3rse

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5 Comments

Nikolay Kuznetsov Over a year ago

I do have proxy in here. But this piece of code prints out "detecting proxies proxy hostname : DIRECT No Proxy" but actually connection to URI specified fails with timeout.

Koray Tugay Over a year ago

proxy hostname : DIRECT No Proxy Does this mean I am not behind a proxy?

splinter123 Over a year ago

same situation, I'm behind a proxy but this I get DIRECT No Proxy using this code...

toolforger Over a year ago

java.net.useSystemProxies does not always work. I don't know all situations where it does nothing, but it will definitely not do anything if the proxy is transparent, i.e. applications just do a direct connection and the proxy will intercept that connection without telling them.

AurysVrV Over a year ago

Worked 1 time and then "Process 'command 'C:\Program Files\Java\jdk-17\bin\java.exe'' finished with non-zero exit value 1"

Jaime Hablutzel · Accepted Answer · 2019-10-01 02:41:02Z

26

This might be a little late, but I ran into the same problem. The way I fixed it is by adding the following system property:

-Djava.net.useSystemProxies=true

Now, note that this property is set only once at startup, so it can't change when you run your application. From https://docs.oracle.com/javase/7/docs/api/java/net/doc-files/net-properties.html#Proxies:

java.net.useSystemProxies (default: false) ... Note that this property is checked only once at startup.

edited Oct 1, 2019 at 2:41

Jaime Hablutzel

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answered Dec 10, 2015 at 14:53

Juan Martin Lichowski

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6 Comments

fragorl Over a year ago

+1 for mentioning that this property is only checked once at startup, something not mentioned anywhere else in this question.

MauganRa Over a year ago

Actually, if this property is specified the system proxy is used automatically!

Michael_S Over a year ago

This does not work with Proxy Auto-Config (PAC) files, see stackoverflow.com/questions/10324996/…

loic Over a year ago

This one helps bypass -javaagent side effects some times (such as Application run in Intellij IDEA)

Joman68 Over a year ago

This does work with PAC files when using java 9 and up - see stackoverflow.com/a/57891805/3059685.

|

Flo · Accepted Answer · 2011-08-16 21:43:09Z

I found an odd behavior experimenting with the suggested code here.

It appears that, after a default ProxySelector has been set, regular socket code (e.g. creating a new Socket) does not work anymore, because it tries to use a socks server (not sure why it would do this, but for me it does).

So if you, when calling

Socket socket = new Socket(host, port);

you receive such a SocketException:

java.net.SocketException: Malformed reply from SOCKS server
    at java.net.SocksSocketImpl.readSocksReply(Unknown Source)
    at java.net.SocksSocketImpl.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at java.net.Socket.<init>(Unknown Source)
    at java.net.Socket.<init>(Unknown Source)

then try setting the default ProxySelector back to null:

ProxySelector.setDefault(null);

For me this resulted in the following small Java class which I now use to simply retrieve the systems proxy settings without having it affect the further usage of Sockets() of the application, yet configuring the system properly to use the proxy:

public class ProxyConfig {

  private static String host;
  private static int port;

  public static void init() {
    System.setProperty("java.net.useSystemProxies", "true");
    Proxy proxy = getProxy();
    if (proxy != null) {
      InetSocketAddress addr = (InetSocketAddress) proxy.address();
      host = addr.getHostName();
      port = addr.getPort();

      System.setProperty("java.net.useSystemProxies", "false");
      System.setProperty("http.proxyHost", host);
      System.setProperty("http.proxyPort", ""+port);

    }
    System.setProperty("java.net.useSystemProxies", "false");
  }

  public static String getHost() {
    return host;
  }

  public static int getPort() {
    return port;
  }

  private static Proxy getProxy() {
    List<Proxy> l = null;
    try {
      ProxySelector def = ProxySelector.getDefault();

      l = def.select(new URI("http://foo/bar"));
      ProxySelector.setDefault(null);
    } catch (Exception e) {
      e.printStackTrace();
    }
    if (l != null) {
      for (Iterator<Proxy> iter = l.iterator(); iter.hasNext();) {
        java.net.Proxy proxy = iter.next();
        return proxy;
      }
    }
    return null;
  }
}

Pops · Accepted Answer · 2011-12-28 16:31:35Z

3

java.net.URL.openStream() is a shorthand for java.net.URL.openConnection().getInputStream().

edited Dec 28, 2011 at 16:31

Pops

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answered Dec 7, 2010 at 13:37

Hrvoje

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Comments

Alain O'Dea · Accepted Answer · 2015-06-08 17:09:37Z

2

UPDATE: you need to have the System Property java.net.useSystemProxies set to true for my solution below to work.

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.

edited Jun 8, 2015 at 17:09

answered Sep 30, 2010 at 12:43

Alain O'Dea

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3 Comments

mmo Over a year ago

Nope - that's not true. Or if it's supposed to work that way it does not work.

Alain O'Dea Over a year ago

@mmo you are correct. Thank you for identifying that. I was using java.net.useSystemProxies and forgot to mention that. It is an essential point.

Alain O'Dea Over a year ago

@mmo have I addressed your concern sufficiently for you to remove the downvote?

Fabio says Reinstate Monica · Accepted Answer · 2018-11-01 21:58:29Z

2

try{
    System.setProperty("java.net.useSystemProxies", "true");
    String prx = ProxySelector.getDefault().select(new URI("http://www.google.com")).get(0).address().toString();
    JOptionPane.showMessageDialog(null, prx);
} catch(Exception e){
    JOptionPane.showMessageDialog(null, "no proxy");
}

edited Nov 1, 2018 at 21:58

Fabio says Reinstate Monica

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answered Nov 1, 2018 at 21:39

Mahdi

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1 Comment

Fabio says Reinstate Monica Over a year ago

Hello, welcome to SO. Your answer contains only code. It would be better if you could also add some commentary to explain what it does and how. Can you please edit your answer and add it? Thank you!

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