Java: cannot access annotations through reflection

Question

Here is a test class:

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;

public class TestAnnotations {

    @interface Annotate{}

    @Annotate public void myMethod(){}

    public static void main(String[] args) {
        try{
            Method[] methods = TestAnnotations.class.getDeclaredMethods();
            Method m = methods[1];
            assert m.getName().equals("myMethod");

            System.out.println("method inspected ? " + m.getName());
            Annotation a = m.getAnnotation(Annotate.class);
            System.out.println("annotation ? " + a);
            System.out.println("annotations length ? "
                + m.getDeclaredAnnotations().length);
        }
        catch(Exception e){
            e.printStackTrace();
        }
    }
}

Here is my output :

method inspected ? myMethod
annotation : null
annotations length : 0

What I am missing to make annotations visible through reflection ?
Do I need an annotation processor even for just checking their presence ?

mykolaj · Accepted Answer · 2015-11-03 14:48:04Z

42

In order to access an annotation at runtime, it needs to have a Retention policy of Runtime.

@Retention(RetentionPolicy.RUNTIME) @interface Annotate {}

Otherwise, the annotations are dropped and the JVM is not aware of them.
For more information, see here.

edited Nov 3, 2015 at 14:48

mykolaj

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answered Feb 18, 2010 at 7:55

abyx

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2 Comments

glmxndr Over a year ago

May I ask, though, if you happen to know whether there is a way to change the default behaviour of CLASS retention policy to RUNTIME ?

user207421 Over a year ago

Only by recompiling the annotation. If it's not your annotation, no.

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