Calling Methods via annotations of unknown classes

I'm currently working on something like a Game engine.
I want it to be modular so that anyone can write a module.
And simply add in a annotations in order to register this class...
Those Modules are basically put into a pool of actions when a specific event gets triggered.
I think that annotations can do what I need for this.
I basically want a function that gets me a random class of all classes with the @actionClass annotation.
Is this possible using annotations or do I need to look for something else?