Hi everybody,
I've been trying to get a hierarchy of classes return defensive copies of
instances of the Java Collections Framework. The idea is, that a caller should
not be able to add/remove elements of a returned List<?> for instance, because
the entity that returned that list should be the one managing it.
I thought of using an aspect, and when trying to do so, I found out that it
works, but it produces quite a bunch of warnings in both my Eclipse workspace
as well as during weaving during a Maven build. I'm wondering if there's
anything I can do to get rid of those warnings.
I wrote the following class to define the aspect (stripped to only contain an
example method):
@Aspect
public final class DefensiveCopyCollectionsReturningAspect {
/**
* Every 'getter' method in the portal model hierarchy that returns a
* {@link List} should return a defensive copy so that calling clients
* don't change the internal structure of the portal model.
*
* @param joinPoint The joinpoint.
* @return An defensive copy of the returned list.
*/
@SuppressWarnings("unchecked", "rawtypes")
@Around("execution(public !static java.util.List<*> (AbstractPM+).get*())")
public List makeDefensiveCopyOfReturnedList(final ProceedingJoinPoint
joinPoint) {
try {
return new ArrayList((List) joinPoint.proceed());
} catch (final Throwable exception) {
throw new PortalRuntimeException(exception);
}
}
}
I've defined methods that do similar things for Set and Map as well, which
works like a charm. However, since the return type of the method is
java.util.List, without any generics involved, I see the following warnings:
-- unchecked conversion when advice applied at shadow
method-execution(java.util.List
com.leanapps.portal.model.pension.participation.ParticipationPM.getDocuments()),
expected java.util.List<com.leanapps.portal.model.report.DocumentPM> but
advice uses java.util.List [Xlint:uncheckedAdviceConversion]
Now here's the million (OK, maybe a little less ;)) dollar question: Is there
any way to get the generics to work? I've tried several things, but they all
don't seem to work. I've tried
<T> List<T> makeDefensiveCopyOfReturnedList(final ProceedingJoinPoint
joinPoint) { .. }
which results in compilation errors:
-- incompatible return type applying to method-execution(java.util.List
com.leanapps.portal.model.pension.participation.ParticipationPM.getDocuments())
If I try to add generics to the annotation:
@Around("execution(public !static java.util.List<T+> (AbstractPM+).get*())")
I see that no advice has been applied at all:
-- advice defined in
com.leanapps.portal.model.DefensiveCopyCollectionsReturningAspect has not been
applied
Hope that somebody on this list has an answer to this.
Kind regards,
Rens
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