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javatypesannotation-processing

Java 6 annotation processing -- getting a class from an annotation

I have an custom annotation called @Pojo which I use for automatic wiki documentation generation:

package com.example.annotations;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.SOURCE)
@Target(ElementType.METHOD)
public @interface Pojo {
    Class<?> value();
}

I use it like this:

@Pojo(com.example.restserver.model.appointment.Appointment.class)

to annotation a resource method so that the annotation processor can automatically generate a wiki page describing the resource and type that it expects.

I need to read the value of the value field in an annotation processor, but I am getting a runtime error.

In the source code for my processor I have the following lines:

final Pojo pojo = element.getAnnotation(Pojo.class);
// ...
final Class<?> pojoJavaClass = pojo.value();

but the actual class in not available to the processor. I think I need a javax.lang.model.type.TypeMirror instead as a surrogate for the real class. I'm not sure how to get one.

The error I am getting is:

javax.lang.model.type.MirroredTypeException: Attempt to access Class object for TypeMirror com.example.restserver.model.appointment.Appointment

The Appointment is a class mentioned in one of my @Pojo annotation.

Unfortunately, document and/or tutorials on Java annotation processing seems scarce. Tried googling.

Solution

  • Have you read this article: http://blog.retep.org/2009/02/13/getting-class-values-from-annotations-in-an-annotationprocessor/ ?

    There the trick is to actually use getAnnotation() and catch the MirroredTypeException. Surprisingly the exception then provides the TypeMirror of the required class.

    I don't know if this is a good solution, but it is one. In my personal opinion I would try to get the type behind the MirroredType, but I don't know if this is possible.