What is the difference between AspectJ And ASM?

Question

As I understand, the 2 frameworks are both static that injects monitor codes into class codes. So, what is the difference?

Lytta

Answer 1

ASM is a framework/library which provides you an API to manipulate existing bytecode and/or generate new bytecode easily.

AspectJ, on the other hand is a language extension on top of the Java language with it's own syntax, specifically designed to extend the capabilities of the Java runtime with aspect oriented programming concepts. It includes a compiler/weaver, which can either be run at compile time or run-time.

They're similar in the sense that both achieve their goals by bytecode manipulation of existing bytecode and/or generating new bytecode.

ASM is more general in the sense that it doesn't have an opinion about how you would want to modify existing bytecode, it just gives you an API and you can do whatever you want with it. AspectJ, on the other hand, is more specific, more narrow scoped, it only supports a few predefined AOP constructs, but it gives you an interface (the aspectj language) which is much easier to work with if you can fit within those constructs it provides you with.

For most use-cases I've seen, AspectJ is more than enough, but in those rare cases where it wouldn't, ASM can be a good alternative, but you'll need more programming work to achieve similar results.

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