Check inheritance of Element in source level AnnotationProcessors

Question

I'm looking for a way to detect if a class is inherited from another class/interface in annotation processor. Since the annotation processor runs on the source code not runtime, there's no way to use reflation API, the only method I found is:

public class MyProcessor extends AbstractProcessor {

    @Override
    public boolean process(final Set<? extends TypeElement> annotations, final RoundEnvironment roundEnv) {
        // Simple test
        processingEnv.getTypeUtils().isAssignable(
                processingEnv.getElementUtils().getTypeElement("java.util.List").asType(),
                processingEnv.getElementUtils().getTypeElement("java.util.Collection").asType()
        );

    }

}

But this method always returns false even though that List implements Collection. Any idea?

Does processingEnv.getElementUtils().getTypeElement("java.util.List") return a sensible type? — Turing85
– Turing85, Commented Dec 26, 2019 at 23:41
Also, could you try using List.class.getCanonicalName() and Collection.class.getCanonicalName() instead of "java.util.List" and "java.util.Collection"? — Turing85
– Turing85, Commented Dec 26, 2019 at 23:48
You're testing if the generic List<E> is assignable to the generic Collection<E>, which is false. In your case, I assume you want to test the raw types—see Types#erasure(TypeMirror). — Slaw
– Slaw, Commented Dec 27, 2019 at 0:05

user1079877 · Accepted Answer · 2019-12-30 09:03:14Z

0

Thanks to Slaw's comment. This solution seems to work:

public class MyProcessor extends AbstractProcessor {

    @Override
    public boolean process(final Set<? extends TypeElement> annotations, final RoundEnvironment roundEnv) {
        // Simple test
        processingEnv.getTypeUtils().isAssignable(
                        processingEnv.getTypeUtils().erasure(processingEnv.getElementUtils().getTypeElement("java.util.List").asType()),
                        processingEnv.getTypeUtils().erasure(processingEnv.getElementUtils().getTypeElement("java.util.Collection").asType())
        );

    }

}

You can find some more information about erasure and what it does in here: https://www.tutorialspoint.com/java_generics/java_generics_type_erasure.htm

answered Dec 30, 2019 at 9:03

user1079877

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