如何将 aspectJ 切入点与动态选择器一起使用？

Question

I'm working on a small project that determines code coverage when testing a java application. It basically consists of a plugin for an IDE which finds all the classes and methods in the project and saves them in a database, and an agent with aspectJ pointcuts that weave around all of these methods to log their execution.

The problem I have is that I only want to log the methods that are actually written by the developers of that very project and not those of underlying libraries. So the pointcuts need to be defined in a way that only methods of classes in the actual project packages are woven. On the other hand, since the agent is to be used with all sorts of projects, I can't hardcode those packages.

My attempt so far was to read all the package names from the database and build a string from that. Basically what it looks like is this:

private static final String POINTCUT_STRING = AspectUtil.buildPointcutString();

And then, when defining the pointcut:

@Pointcut(POINTCUT_STRING)

Thing is, this doesn't work because apparently when defining a Pointcut, the

Attribute value needs to be a constant.

So, how can I make it so that i can only weave methods in classes in the packages that I have in my database?

Thanks in advance, have a good one!

Answer 1

I don't think a dynamic aspect approach is going to work as aspectj does not expose the weaver to any state management or changes. Although this would be theoretically possible at runtime it's definitely not possible at compile time (and you have the option to add your aspects at compile time).

But to your issue...

What weave strategy are you using? compile or runtime? I've found compile to work very well and I'm not sure how to use runtime with aspectj. But what I can say is that if you use compile you'll only be weaving the application classes in any case as that is all you'll have access to.

Another comment to make is if you want to do something dynamic you'd be better off putting the condition on whether to monitor that method for code coverage downstream of the aspect. So when the aspect is executed the first thing it will do is decide if this class/method call should be monitored for coverage and then go on from there...

Answer 2

When I asked you:

What do you mean by "runtime weaving"? Load-time weaving (LTW) maybe? Ie you are using aop.xml ? I am asking for a specific reason.

You replied:

Yes, LTW. I am using an aop.xml file.

In that case you have the option of specifying pointcut definitions in aop.xml which is read during JVM start-up when the weaving agent is activated. For refererence, please read the AspectJ Developers Guide, there is a chapter on LTW . You will find sample code and sample XML definitions there, showing how you can extend an abstract aspect with an abstract pointcut in the XML file and specify a concrete pointut for a concrete subclass. That should give you the options you need to keep your pointcut out of the Java code, for whatever reason you think that's a good thing and you need it.

Please note that you cannot expect to modify aop.xml during runtime and re-load it, possibly re-applying the aspect dynamically to all classes. AspectJ LTW works in connection with class-loading, ie you only have one shot at JVM start-up before all application classes are loaded. This is not an AspectJ limitation but just how bytecode instrumentation in the JVM works.