Get list of fields with annotation, by using reflection

Question

I create my annotation

public @interface MyAnnotation { } 

I put it on fields in my test object

public class TestObject {      @MyAnnotation      final private Outlook outlook;     @MyAnnotation      final private Temperature temperature;      ... } 

Now I want to get list of all fields with MyAnnotation.

for(Field field  : TestObject.class.getDeclaredFields()) {     if (field.isAnnotationPresent(MyAnnotation.class))         {               //do action         } } 

But seems like my block do action is never executed, and fields has no annotation as the following code returns 0.

TestObject.class.getDeclaredField("outlook").getAnnotations().length; 

Is anyone can help me and tell me what i'm doing wrong?

Answer 1

You need to mark the annotation as being available at runtime. Add the following to your annotation code.

@Retention(RetentionPolicy.RUNTIME) public @interface MyAnnotation { } 

Answer 2

/**  * @return null safe set  */ public static Set<Field> findFields(Class<?> classs, Class<? extends Annotation> ann) {     Set<Field> set = new HashSet<>();     Class<?> c = classs;     while (c != null) {         for (Field field : c.getDeclaredFields()) {             if (field.isAnnotationPresent(ann)) {                 set.add(field);             }         }         c = c.getSuperclass();     }     return set; }