Get notified when annotated objects are created in Java

Intent

I've got a custom Java annotation: @DynamicField

public class RESTEndpointInvoker {
  @DynamicField(key="httpTimeout")
  private long httpTimeout = 8000L;

  public void setHttpTimeout(long t){
    this.httpTimeout = t;
}

When someone changes a value in a file or database corresponding to the annotated field, invoke the setter for all instances with that property to reflect the new value. So I need to keep track of all instances that use the annotation, in a map or something, to update them when a change occurs externally:

Map<Key,List<Instance>>

Note: I intend to use some form of WeakHashMap() to avoid holding references to stale instances.

Question

How do I track annotated, but arbitrary, instances if I don't control when and how those instances are created?

Ideally, I want to be notified the moment an instance is created.

Tried

I can scan the classpath for class types, then search each class for annotated fields (see below), but I'm not sure how to track live instances.

  //get classes with annotation
  Reflections r = new Reflections("com.foo", new TypeAnnotationsScanner());
  Set<Class<?>> allAnnotated = r.getTypesAnnotatedWith(DynamicField.class);
  //identify fields
  for(Class<?> cls : allAnnotated){
    for(Field field : cls.getDeclaredFields()){
    Class type = field.getType();
    String name = field.getName();
    if(field.isAnnotationPresent(DynamicField.class)){
      ....
    }
  }
}

Solution for Spring beans

If those instances are spring beans, I can do it, but I'd rather avoid that limitation.