Cross cutting concern example

Question

What is a good example of a cross-cutting concern? The medical record example on the wikipedia page seems incomplete to me.

Specifically from this exam

Answer 1

I think the single best example of a cross-cutting concern is transactional behavior. Having to put try-catch blocks with commit and rollback calls in all your service methods would be repellent, for instance. Annotating the methods with a marker that AOP can use to encapsulate them with the desired transactional behavior is a big win.

Another good candidate as an example of a cross-cutting concern is authorization. Annotating a service method with a marker that tells who can call it, and letting some AOP advice decide whether to allow the method call or not, can be preferable to handling that in service method code.

Implementing logging with AOP advice could be a way to get more flexibility, so that you can change what gets logged by changing a joinpoint. In practice I don't see projects doing that very often. Typically using a library like log4j that lets you filter by logging-level and category, at runtime if you need to, works out well enough.

A core concern is a reason that the application exists, the business logic that the application automates. If you have a logistics application that handles shipping freight, figuring out how much cargo you can pack on a truck or what's the best route for the truck to take to drop off its deliveries might be core concerns. Cross-cutting concerns are typically implementation details that need to be kept separate from business logic.