Java Imports, Assembly (Krakatau), and Source Code

Question

So here's my situation:

I am running a Java Client/Server architecture that has high CPU usage and I'm trying to reduce the lag time on the main "server" thread. I have been profiling the server with YourKit to identify the CPU-hogging code.

The problem is:

I am using someone else's code, and because of the way it is written, it is impossible to decompile, then recompile without using a special obfuscator which I do not have access to (no I am not violating any copyrights or anything).

What I am currently doing:

To modify the class files without worrying about obfuscation, I have been using Storyyeller's amazing Krakatau decompiler (https://github.com/Storyyeller/Krakatau) to disassemble class files into assembly files.

I manually edit the .j assembly files while looking at a Jasmin reference page (which takes FOREVER and I often mess up), then reassemble them into class files and run them again.

What I want to do:

Instead of painstakingly editing the assembly, I was wondering, does anyone know of a way to convert .java Source Code to .j Assembly code?

Also, if I simply decompile the .class files, is it possible for me to simply recompile them even though the packages for the imports do not exist?

import com.bazinga.*;
public class MainThread{}//compile this even though package com.bazinga doesn't exist?

If anyone knows ANY WAY I could do this, I would really appreciate it!

Does the current LICENSE prohibit exactly what you are doing now? If so, you may want to contact the copyright holder to work out a deal. — Thorbjørn Ravn Andersen, Jan 16 '15 at 20:42
No, it is not prohibited, there's no need to worry about that, it isn't illegal — Sameer Puri, Jan 16 '15 at 20:48
The copyright holder may then help you with actual source, which hopefully should make this much easier to do. — Thorbjørn Ravn Andersen, Jan 16 '15 at 21:19
The thing is, the holder has abandoned the project...I have tried contacting him but have received no response — Sameer Puri, Jan 16 '15 at 21:32
This is why you need source for all your software dependencies (or very good commercial licenses) so you don't have to work like this later. I would suggest replacing the troublesome code with another library if at all possible. — Thorbjørn Ravn Andersen, Jan 18 '15 at 01:40

score 1 · Answer 1 · answered Nov 05 '16 at 22:10

Instead of painstakingly editing the assembly, I was wondering, does anyone know of a way to convert .java Source Code to .j Assembly code?

Yes and no. The obvious answer is that you can just compile your code and then disassemble the resulting classes. However, this is not always helpful, because compilation can be context dependent (such as inlining static final constants, or handling of nested classes). Additionally, if you plan to add your code into an existing method, you have to be careful to not use existing local variable slots or clobber the operand stack.

My best advice is to try to isolate your modifications as much as possible. For example, if you want to add code to the jar, instead of inserting it into an existing class, just write the code you want to add in Java, compile it and add the classfiles in. Then modify the target class to call into your own class.

As for imports, you can compile against stubs. Just create a dummy class with the name you want, and optionally dummy methods for anything you need to call. The implementations can just be {throw null;} or similar, since you won't actually be executing them ever, they just need to exist to satisfy the compiler during compilation.

Java Imports, Assembly (Krakatau), and Source Code

1 Answers1