How to patch Java bytecode?

Question

Java

The task is this: there are obfuscated classes.
Tried to decompile, reverse compilation does not lend itself to this.
You need to insert a pair of System.out.println into the code to display dumps.
Tried patching bytecode with jbe and reJ.
Both tools are outdated, work with errors and do not give the desired result.
What other tools can be used to work with bytecode?

Answer 1

https://github.com/cglib/cglib

Answer 2

jd.benow.ca for example