Get list of fields with annotation, by using reflection

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?

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小开

最佳答案

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

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

小开

/**
* @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;
}