Detecting Windows/IE proxy setting using Java

Question

I need to automatically detect if a user requires a proxy to access the internet. Is there a way for a Java application to read the systems proxy setting?

Thanks, Jimmy

Answer 1

Java SE 1.5 provides ProxySelector class to detect the proxy settings. If there is a Direct connection to Internet the Proxy type will be DIRECT else it will return the host and port.

Example below illustrates this functionality:

import java.net.InetSocketAddress; import java.net.Proxy; import java.net.ProxySelector; import java.net.URI; import java.util.Iterator; import java.util.List;  public class TestProxy {      public static void main(String[] args) {         try {             System.setProperty("java.net.useSystemProxies","true");             List<Proxy> l = ProxySelector.getDefault().select(                         new URI("http://www.yahoo.com/"));              for (Iterator<Proxy> iter = l.iterator(); iter.hasNext(); ) {                  Proxy 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.out.println("proxy port : " + addr.getPort());                 }             }         } catch (Exception e) {             e.printStackTrace();         }     } } 

Answer 2

The other, accepted, answer is undoubtedly excellent and correct but I thought I would add something here...

If you are on a machine that is configured with "auto detect proxy settings", which I believe is called PAC, the code to detect the proxy in the answer using the Java gubbins will not work (it will think it is a "direct" connection).

There is a library called proxy vole (new BSD license I think), however, that you can use instead so here's the other answer's code slightly modified to use that:

public class testProxy {         public static void main(String[] args) {         try {                 System.setProperty("java.net.useSystemProxies","true");              // Use proxy vole to find the default proxy             ProxySearch ps = ProxySearch.getDefaultProxySearch();             ps.setPacCacheSettings(32, 1000*60*5);                                          List l = ps.getProxySelector().select(                     new URI("http://www.yahoo.com/"));              //... Now just do what the original did ...             for (Iterator iter = l.iterator(); iter.hasNext(); ) {                 Proxy proxy = (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.out.println("proxy port : " +                              addr.getPort());                     }             }         } catch (Exception e) {             e.printStackTrace();         }             } } 

It needs these imports:

import java.net.InetSocketAddress; import java.net.Proxy; import java.net.URI; import java.util.Iterator; import java.util.List;  import com.btr.proxy.search.ProxySearch; 

Oh, and there're usage examples for proxy vole here.