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Expertise: Intermediate
Language: Java

July 2, 2001

Setting Proxy in Java Code

The java.net package contains classes that deal with connections across the network. If there is a direct connection to the Internet via a modem, various classes like the HttpConnection or the raw Connection class can be used to get a connection to a server on the net.

This approach fails if you are going through a proxy server. To tell the JVM a proxy is installed, system variables need to be set explicitly set using the System class.

What you have to do is basically set three variables. These are:

 
    proxySet
    proxyPort
    proxyHost

This small piece of code shows how to set a proxy before calling the connecting code:

 
//some previous code

    System.getProperties().put(“proxySet”,”true”);
    System.getProperties().put(“proxyPort”,”8080”);
    System.getProperties().put(“proxyHost”,”host”);
    try
    {
          URL validateURL = new URL(“www.foo.com?name=Irfan”);
          URLConnection connection = validateURL.openConnection();
          //Do some thing with the connection

    }
    catch(Exception e)
    {
        //Show the Exception
    }

//Rest of the stuff....

If the connection is being rooted through a proxy and you don’t set the above system variables, you will most likely get the familiar java.net.UnknownHostException.