On your way in you may have missed that JavaRanch has a policy on display names, and yours does not comply with it; specifically, a first name and a last name are required. Please adjust it accordingly, which you can do right here. Thanks for your prompt attention to this matter. [ August 02, 2006: Message edited by: Ulf Dittmer ]
If you have access to the sources of the JDK tools, you could study the "jar" tool, which can update existing jar files. It might have some useful helper classes that augment the java.util.jar package in this regard.