AspectJ - Weaving with custom ClassLoader at runtime

问题:

I'm trying to load classes at runtime and weave them with some AspectJ aspects at this point. I have load-time weaving enabled, and it works when I use it more conventionally.

I have the following in my @Aspect class:

@Before("call(* mypackage.MyInterface.*())") public void myInterfaceExecuteCall(JoinPoint thisJoinPoint,         JoinPoint.StaticPart thisJoinPointStaticPart,         JoinPoint.EnclosingStaticPart thisEnclosingJoinPointStaticPart) {     System.out.println(thisJoinPoint.getSignature().getDeclaringType());     System.out.println(thisJoinPoint.getSignature().getName()); } 

Then I'm scanning the jars and finding classes that are implementations of MyInterface:

URLClassLoader classLoader = new URLClassLoader(new URL[] { urlOfJar },         ClassLoader.getSystemClassLoader()); WeavingURLClassLoader weaver = new WeavingURLClassLoader(         classLoader); HashSet<Class<?>> executableClasses = new HashSet<Class<?>>(); for (String name : classNamesInJar) {     try {         Class<?> myImplementation = weaver.loadClass(name);         if (MyInterface.class.isAssignableFrom(myImplementation)) {             executableClasses.add(myImplementation);         }     } catch (Exception e) {         e.printStackTrace();     } catch (NoClassDefFoundError e) {         e.printStackTrace();     } } 

... and then I'm executing a specific method in the loaded classes at some point:

try {     Method execute = myImplementation.getMethod("execute");     execute.invoke(myImplementation.newInstance()); } catch (Exception e) {     e.printStackTrace(); } 

However, the @Before method that I gave you above is never executed when I call execute.invoke(...) (although the execute method itself is obviously executed, since I see its output).

Does someone know what I'm doing wrong? What's the way to make myInterfaceExecuteCall get called before the loaded class's methods get called?

回答1:

OK I found out what it was, and it doesn't work quite the way I intended it, but here is a workaround:

Just do a @Before("execution(* mypackage.MyInterface.*())") instead of call. This works even if the class was loaded manually and at runtime by a custom class loader. This is because AspectJ doesn't care about calls that are done with using Method.invoke(...). I hope someone else can use this workaround.

Here is a link to the documentation containing the memorable info:

For example, the call pointcut does not pick out reflective calls to a method implemented in java.lang.reflect.Method.invoke(Object, Object[]).

http://www.eclipse.org/aspectj/doc/released/progguide/implementation.html

If you have a different solution, please don't hesitate to answer!

回答2:

If I'm not mistaken, AspectJ can't weave JDK classes. That would explain this:

For example, the call pointcut does not pick out reflective calls to a method implemented in java.lang.reflect.Method.invoke(Object, Object[]).

文章来源: AspectJ - Weaving with custom ClassLoader at runtime