Java how to extract from a jar and put classes back into working project?

I am trying to take files from a jar that is part of a working project, and put them back in to the project so I can run it while making subtle changes to the classes.

I have read it is possible to extract a jar, decompile, edit, reassemble the jar and run the project, but I dont want to do all that every time I make a small edit.

I have tried extracting and decompiling the jar, and then creating a new package in eclipse with the same name as the original jar, and then adding all the files back in; however I get hundreds of errors.

I am very new to java and I realize this is beyond my current skill level, so any help is greatly appreciated if there is a simple way to do this. None of the other threads on this give a clear answer.


Compilation and decompilation are lossy processes, so in general, you can't expect to be able to re-compile decompiled code. If you want to make changes to an application and run the modified version, your best best is disassemble it with Krakatau, edit the assembly file, and reassemble. The Krakatau assembly format is designed to be very close to the classfile format, so you can make changes without disrupting everything. The downside is that you have to understand Java bytecode.

I'd also suggest checking out Konloch's Bytecode Viewer or Samczsun's Helios, which might be able to do what you want.

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