Question

I want to add annotations on my classes properties, and then iterate all my properties with the ability to lookup the annotations also.

So for example, I have a class like:

public class User {

   @Annotation1
   private int id;
   @Annotation2
   private String name;
   private int age;

   // getters and setters
}

Now I want to be able to loop through my properties, and be able to know what annotation (if any) is on the property.

I want to know how to do this using just java, but also curious if using either spring, guava or google guice would make this any easier (if they have any helpers to do this easier).

Answer 1

Here is an example that utilizes the (barely maintained) bean instrospection framework. It’s an all Java solution that you can extend to fit your needs.

public class BeanProcessor {
   public static void main(String[] args) {
      try {
         final Class<?> beanClazz = BBean.class;
         BeanInfo info = Introspector.getBeanInfo(beanClazz);
         PropertyDescriptor[] propertyInfo = info.getPropertyDescriptors();
         for (final PropertyDescriptor descriptor : propertyInfo) {
            try {
               final Field field = beanClazz.getDeclaredField(descriptor
                     .getName());
               System.out.println(field);
               for (final Annotation annotation : field
                     .getDeclaredAnnotations()) {
                  System.out.println("Annotation: " + annotation);
               }

            } catch (final NoSuchFieldException nsfe) {
               // ignore these
            }
         }
      } catch (Exception e) {
         e.printStackTrace();
      }
   }
}