问题
I would think this question have been asked before, but I was not immediately able to find related SO questions, or articles elsewhere for that matter.
It strikes me that certain terms in AOP are rather strange. It seems I'm not the only one - this article, for instance, notes that "unfortunately, AOP terminology is not particularly intuitive". However, I have not found a resource explaining why they are not more "intuitive", if that's possible.
More specifically: I can somewhat understand "aspect" and "join points" - they seem descriptive enough. But "pointcuts" and "advice" seem somewhat odd. How did these terms come about?
I think knowing the etymology of these terms will help in remembering them better, if not allowing for some insight into the thinking of AOP's designers. At least, I hope this will help me from ever blubbering out nonsensical things like "cut points" or "advice points" in meetings...
回答1:
Totally agree with your frustration. Each terminology has it's use but everytime I have to deal with AOP I sometimes have to refresh my memory on what each terminology does.
What helps me is that the whole AOP is based on single concept of Method interceptor that can be applied to method, can decide if it needs to take action on that method call and apply custom logic to before and after that method call.
Take a look at Springs org.aopalliance.intercept.MethodInterceptor and it's inheritance hierarchy. For example the advice is actually an abstract definition of MethodInterceptor and pointcut is the logic of selecting to which methods to apply that advice (or MethodIntercptor).
As far as I can remember even pointcut is just another method interceptor that delegates to a method interceptor.
回答2:
Etymology will not help much. You will just have to learn the terminology. But as for historical information about how some terms came about to be used, maybe you need to perform a web search, it is not really a question for StackOverflow. At least I found some background info about the term advice for you.
Update: Actually there are not so many technical terms you need to be familiar with. The following is from one of my AOP slides. I use them in order to introduce AOP to developers when coaching them:
What is an aspect?
- An aspect contains all necessary elements to implement a cross-cutting concern in a modular way. So, it is much like what a class is for a core concern.
- An aspect can, like a class, contain some kind of "methods" called advice and data. It can be a singleton or instantiated multiple times, depending on its usage.
- Because an aspect is defined independently of the core system, we need something else to weave its orthogonal functionality into the core code. This something is called a pointcut and determines where an advice should be applied, e.g. before or after certain method calls, upon an exception, when an object is created and so forth.
- Any place or event in the core code where aspect code can potentially be woven in is called a joinpoint.
If you need a crib or memory hook, maybe this helps (please note the words in italics):
- The aspect method which advises the core code about how to apply a cross-cutting concern, is called advice.
- Each point in your core code which you can hook into in order to apply a cross-cutting concern, is called a joinpoint.
- You cut a slice (or subset) off of your core code joinpoints by means of a query syntax (like SQL selects table rows) called pointcut.
I do not know if this is helpful, but I hope so.
来源：https://stackoverflow.com/questions/43971523/origin-of-some-of-aops-terminology