Get package name and parametrized type from a field element - Annotation Processor

Question

How can I get package name, generic type and Parametrized type from a type from a field element in Annotation processor?

Say, if Element.asType returns java.util.List<String>, I want to get

• Package name java.util
• Generic type List<E> or raw type List (preferably raw type)
• Actual Type String

Is there any method in element utils, type utils?

Gamine

Answer 1

Getting the package java.util:

Element        e   = processingEnv.getTypeUtils().asElement(type);
PackageElement pkg = processingEnv.getElementUtils().getPackageOf(e);

Getting the raw type List:

TypeMirror raw = processingEnv.getTypeUtils().erasure(type);

Getting the type arguments e.g. String:

if (type.getKind() == TypeKind.DECLARED) {
    List<? extends TypeMirror> args =
        ((DeclaredType) type).getTypeArguments();
    args.forEach(t -> {/*...*/});
}

See: Types.asElement, Elements.getPackageOf, Types.erasure and DeclaredType.getTypeArguments.

Litton

Are there any consequences of comparing DeclaredType with instanceof and element.asType().getKind() == TypeKind.DECLARED)? – Gamine

If you needed to be sure that the type really is a declared type, then getKind() probably is more technically correct. The documentation requires that an empty list be returned if there are no type arguments so whether or not it would be an error not to is a bit ambiguous. On the other hand, if you have a TypeElement, then you don't need to check since it will always be a DeclaredType. – Litton