you can annotate a method in you Entity class by @PostLoad to set default value to ...
if you annotate you ID class, then you need to introduce it as Callback Listener in your Entity class :
@EntityListeners({ID.class})
class MyEntity
and i don't think its a good idea, because the instance of your Listener is not related to the Instance of ID in your Entity class. they are 2 different object of ID class.
@PostLoad
Is used to specify callback methods
for the corresponding lifecycle event.
This annotation may be applied to
methods of an entity class, a mapped
superclass, or a callback listener
class.