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?
Load-time weaving (LTW) is simply binary weaving defered until the point that a class loader loads a class file and defines the class to the JVM. To support this, one or more "weaving class loaders", either provided explicitly by the run-time environment or enabled through a "weaving agent" are required.
Weaving in AspectJ Classes are defined using Java syntax. The weaving process consists of executing the aspect advice to produce only a set of generated classes that have the aspect implementation code woven into it.
What AspectJ does is always pretty much the same: It modifies Java byte code by weaving aspect code into it. In case 1 you just get one set of class files directly from ajc . Case 2.1 creates additional, new class files. Case 2.2 just creates new byte code in memory directly in the JVM.
AspectJ Provides a Standard Mechanism to Handle a Crosscutting Concern. In the example shown above, we are doing a null validation and throwing an IllegalArgumentException when the request is null. This way we make sure that whenever an argument is null, we get the same uniform behavior.
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!
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