What's a good free bytecode editor? I want an editor, something with a GUI...
I tried jbe-0.1b with no luck (can't save the bytecode changes).
Nothing decent with a UI, but you can use the Eclipse Bytecode Outline plugin to turn any Java class into ASM code, edit it, and produce the changed class. It's probably the most painless way at the moment.
I understand jasmin and jasper are the usual pair used to translate between bytecode and an assemly language representation.
IIRC, Apache BCEL comes with a tool to disassemble class files to code which creates the class file with BCEL.
I've used vi. :)
Just to be sure. Have you tried to decompile the class files? I don't know what are you trying to do exactly, but you could first decompile the classes, edit the sources and recompile again.
JAD is a very good decompiler which can handle pretty ugly bytecode and produce readable sources from it.
To create java bytecode you could use ASM which offers also eclipse plugins.
ASM is an all purpose Java bytecode manipulation and analysis framework. It can be used to modify existing classes or dynamically generate classes, directly in binary form.
来源：https://stackoverflow.com/questions/2395574/java-bytecode-editor