Is it possible to modify the bytecode and save it with javassist?

All the references I've found on the web says the byte开发者_如何转开发code can be modified at runtime, but I don't seem to find if that modified bytecode could replace the original.

This way the original bytecode could be substituted once, and the rest of the time, use the enhanced afterwards.

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Yes, it's called build-time byte-code instrumentation; javassist as well as libraries such as aspectj supports this model.

I've had good experience with the latter in combination with Apache Maven using the aspectj-maven-plugin.

[Edit] Also see the Implementing Build-time Bytecode Instrumentation With Javassist article.