How to load a resource from compound JAR?

I have the following problem:

I am writing an application that uses some of the JARs from the Netbeans Platform. To be exact, I am only using the Netbeans Visual Library for creating some graphs. This can be done without using the Netbeans Platform by extracting 3 JARs from the platform. This is all working well, except for 1 problem.

Some Background

I am using the Java Simple Plugin Framework (JSPF) to handle my plugin management. So I have an application that basically consists of a skeleton framework, and then depending on which plugin JARs it finds, it can do various things, one of which is drawing graphs. The JAR plugin for this functionality has all it's dependant libraries inside. This is done by exporting the JAR as an artifact in IntelliJ, which will unJAR all the dependant libraries and reJAR them inside yours (so everything you need is there).

The Problem

What seems to be happening t开发者_JAVA百科hough, is that when it tries to start use the classes from the embedded libraries, it works fine, but when it needs resources (.png specifically in my case), it complains that it cannot find it.

My Thoughts

The only thing I can think of why it is not working, is that it could be since the plugin JAR is not in a classpath. Could this be it?

Is there anyway to specify a classpath directory in the MANIFEST maybe? Otherwise must I create my own ClassLoader and manually load all the JARs in the plugins directory?

Thank you!

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UPDATE:

I have subsequently pinpointed that it is indeed a problem with the classpath. If I place my compound library on the classpath, everything works perfectly. The problem I experience now though is:

1. If I copy the library to /Library/Java/Home/lib/ext/ it works fine. If I execute the application with java -cp "/path/to/plugins/myLib.jar" -jar Application.jar it does not work.
2. How can I load all the jars in the plugins directory into my application so the resources inside them can be used?

Thanks again!

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So I have finally figured out what was happening. When creating a executable jar, the MANIFEST.MF file overrides any classpath you specify in the command-line, which basically renders it useless if you want to specify external jars. This seems to be a general problem that has been logged since Java 1.3 already.

My simple solution is to simply not create a executable jar, and then launch the application with a script:

java -cp App.jar:plugins/* my.package.structure.App

which works perfectly.

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The default classloader's do not load classes in nested jars. You'll need to write your own classloader to get the classes in the nested jars.

You can check out this jspf article...

"I forgot: Adding dependencies as JARs inside JARs is not possible, because it would not work in all scenarios (e.g., applets); IIRC also tools like Eclipse would have problems if you used classes with unresolved (read: runtime-resolved-dependencies). To my knowledge there is no established way yet to gracefully handle nested JARs in all circumstances."

http://code.google.com/p/jspf/wiki/UsageGuide