All entries for Monday 13 February 2006

helloworld annotation

So I wanted to play around with Annotations, so I decided to do a hello world.

Actually, the use case is I wanted to mark hibernate backed objects as needing to be autowired by Spring.

public @interface Autowired {
}

and updated my class:

@Autowired public class MyClass {
}

and nothing. The unit test failed:

        MyClass cf = new MyClass();

        Class class1 = cf.getClass();
//        assertTrue(class1.isAnnotationPresent(Autowired.class));
        Annotation[] anns = class1.getAnnotations();
        assertEquals(1, anns.length);

No idea why, thinking it might be a class path issue with Eclipse, I recompiled, but still nothing.

As it turns out, you need to annotate your annotations :) You need to tell the compiler how to retain the annotations (link).

Specifying that the annotations must be retained for runtime retrieval means it now works:

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Autowired {
}

The Target BTW restricts this annotation so it can only be applied to a class.

Very useful stuff :)

: 13 Feb 2006 17:48 |  Tags: Annotations Java Tiger |  Comments (2) |  Close comments |  Report a problem