ASM

Having a choice between SAX-like and DOM-like iteration over classes' bytecode, and having a dead-simple API, is just what I was looking for - and ASM provided.

I've only used the core, SAX-like API, so my comments are based on that.

There were no more chasing after instruction handles (for jumps) or manually keeping track of the constants pool.

The additional tools library provides a great tracing tool which allows you to watch the bytecode before and after the manipulation - a great tool for debugging, and together with the chaining ability, I only had to optionally chain the tracer to the rest of the manipulators, keeping the manipulation modules free of debug and trace code.

Warmly recommend this for anything involving bytecode.