Sunday, March 13, 2022

[SOLVED] APT How to process annotations of nested annotated classes

Issue

I am trying to write an annotation processor using java. This annotation processor needs to identify annotated nested classes within an annotated class as seen below. I will process the annotated classes first then process their inner annotations. This is performed at compile time and I will have no existing knowledge of the class being processed. It is possible to have multiple nested classes within Foo. How do I process the annotations of all these nested classes.

@MyAnnotation(value="Something important")
public class Foo
{
    private Integer A;

    @MyMethodAnnotation(value="Something Else")
    public Integer getA() { return this.A; }

    @MyAnnotation(value="Something really important")
    private class Bar
    {
        private Integer B;

        @MyMethodAnnotation(value="Something Else that is very Important")
        public Integer getB() { return this.B }     
    }
}

How can I get access to the nested Bar class, it's annotation 'MyAnnotation' and its 'MyMethodAnnotation' during processing? The following code only prints out information about class Foo. How can I process information about Bar?

for (Element element : env.getElementsAnnotatedWith(MyAnnotation.class)) {
    if ( element.getKind().equals(ElementKind.CLASS) )
    {
        System.out.println(element.getKind().name() + " " + element.getSimpleName() );
        processInnerClassElement(element);
    }
    else
    {
        System.out.println(element.getKind().name() + " " + element.getSimpleName() );
    }    
}

...


private void processInnerClassElement(Element element)
{
    for (Element e : element.getEnclosedElements() )
    {
        if ( e.getKind().equals(ElementKind.CLASS) )
        {
            System.out.println(e.getKind().name() + " " + e.getSimpleName() );
            processInnerClassElement(e);
        }
        else
        {
            System.out.println(e.getKind().name() + " " + e.getSimpleName()  );
        }
    }
}

Solution

I guess it depends how these annotation relate to each other.

You could simply declare all the annotations in @SupportedAnnotationTypes and have several blocks in the process-method like:

for (Element element : roundEnv.getElementsAnnotatedWith(MyAnnotation.class)) {
    MyAnnotation myAnnotation = element.getAnnotation(MyAnnotation.class);
    if (myAnnotation != null) {
        doSomething(myAnnotation, element);
    }
}

for (Element element : roundEnv.getElementsAnnotatedWith(MyMethodAnnotation.class)) {
    MyMethodAnnotation myMethodAnnotation = element.getAnnotation(MyMethodAnnotation.class);
    if (myMethodAnnotation != null) {
        doSomething(myMethodAnnotation, element);
    }
}

Otherwise you might be able to use element.getEnclosedElements() and element.getEnclosingElement() to achieve what you want.



Answered By - Puce
Answer Checked By - Marilyn (WPSolving Volunteer)
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