Java Programming

Hello,
I'm looking for an obfuscation tool that doesn't work on bytecode file but directly on the source code. It could seem a weird request, I'll explain my problem...

I developed a GWT Java application and I'm packaging it in a jar file for reuse and commercial distribution, GWT requires that a jar file containing a module must contain the .java files together with .class files for the client-side of the application. It is not easy protect the code in such context, the only thing I can do is obfuscate the source code but with a "lighter" obfuscation algorithm that preserves the public interface of my classes, the packages, the imports and all the parts of code that shouldn't be changed to make the code be compiled.
The tool i'm looking for should execute that "light obfuscation" task as an ant task before creating the jar file so that I can work over the code as usual...

could anyone help me?