Find type parameter of method return type in Java 6 annotation processor

I'm writing a tool that uses the annotation processor to generate source code depending on the return type of methods of an annotated class. The return type is always some subtype (interface or class) of an interface A that defines a type variable T.

interface A<T>{T m();};

I would like to find the type parameter for the method m() return value type variable T.

The return type is represented by the annotation processor as a javax.lang.model.type.TypeMirror instance. The simplest case is to return A<T> directly.

@SomeAnnotation
class SomeClass{
    A<T> x();
}

The processor code to find out T is quite simple. (I'll cast instead of using the visitor API here to keep the code simple.)

DeclaredType type = (DeclaredType) typeMirror;
TypeMirror t = type.getTypeArguments().get(0);

The TypeMirror of the return type is a javax.lang.model.type.DeclaredType and T is the first type argument. The result t is a javax.lang.model.type.TypeVariable for T. The same works for a concrete return type A<B> (B is some type: interface B{}). The result for t is a DeclaredType representing B.

Things start to get complicated with other result types:

interface Subtype<T> extends A<T>{}
interface Concrete extends A<B>{};
interface Multiple<B,T> extends A<T>{}
interface Bounds<T extends B> extends A<T>{}
interface Hierarchy extends Concrete{}

                        
                        java
                        
                        generics
                        
                        annotations
                        
                        annotation-processing

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 public AnnotationProcessor getProcessorFor(
            Set<AnnotationTypeDeclaration> atds,
            AnnotationProcessorEnvironment env) {
        return new SomeAnnotationProcessor(env);
    }

    private static class SomeAnnotationProcessor implements AnnotationProcessor {
        private final AnnotationProcessorEnvironment env;

        SomeAnnotationProcessor(AnnotationProcessorEnvironment env) {
            this.env = env;
        }

        public void process() {
            for (TypeDeclaration typeDecl : env.getSpecifiedTypeDeclarations()) {
                System.out.println("in class: " + typeDecl);
                typeDecl.accept(getDeclarationScanner(
                        new SomeClassVisitor(), NO_OP));
            }
        }

        private static class SomeClassVisitor extends SimpleDeclarationVisitor {
            @Override
            public void visitMethodDeclaration(
                    MethodDeclaration methodDeclaration) {
                System.out.println("visiting method: "+methodDeclaration + " -> "+methodDeclaration.getReturnType());
                methodDeclaration.getReturnType().accept(new SomeTypeVisitor());
            }
        }
    }

    private static class SomeTypeVisitor implements TypeVisitor {

        public void visitClassType(ClassType classType) {           
            System.out.println("classType: " + classType + " -> "+classType.getClass());                
        }

        @Override
        public void visitInterfaceType(InterfaceType interfaceType) {
            Types types = annotationProcessorEnvironment.getTypeUtils();
            TypeDeclaration typeDeclaration = annotationProcessorEnvironment
                    .getTypeDeclaration("A");           
            Collection<InterfaceType> superinterfaces = interfaceType
                    .getSuperinterfaces();                      
            System.out.println("interfaceType: " + interfaceType + " -> "


                        
                        
                            answered 2009-09-09T13:36:41.487

Find type parameter of method return type in Java 6 annotation processor

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