What are the possible AOP use cases?

I can give you two examples where we use it:

• Automatically registering objects in JMX for remote management. If a class is annotated with our @AutoRegister annotation, we have an aspect that watches for new instantiations of that class and registers them in JMX automatically.

• Audit logging (the gold standard AOP use case). Its a bit coarse but the general approach is to annotate methods that represent some auditable action. Combined with something like Spring Security, we can get a pretty good idea of:

  • who the user is
  • what method they're invoking
  • what data they're providing
  • what time the method was invoked
  • whether the invocation was successful or not (i.e., if an exception was thrown)

• Exception Handling: don't need to repeat the horrible list of try ... catch, catch, catch etc - also means the exception handling is guaranteed to be consistent.
• Performance monitoring: Very useful as using an aspect is non intrusive and can be done after the fact and then turned off when no longer required.

Wow... 10 years ago - didn't have much for AOP... Here are a few more

• Be able to customise objects where you don't have access to their constructor (e.g. jpa entities)
• Implementing security rules (security says user is not allowed to call this method - AOP can implement that)
• Transaction manager (begin, commit, rollback)
• Caching - want to cache the result of a method and not call it again

To see the coverage of AOP in terms of applicability I really recommend you to read the book Aspect-Oriented-Software-Development-Use-Cases. This book elaborates use cases of functional and non-functional requirements using AOP. After that you will see that aspects can be used to more requirements than logging, tracing, security, etc.