This code does work, but I am looking for something more generic as I will need to perform various different tasks for different fields on different entities.

To determine whether any field has changed on any entity, I would potentially have to add code to all my set methods to flag the field as dirty.

I managed to get around the problem for now by creating 2 new instances of the entity. One is used to store the current state of the entity and the other is used to store the state of the entity after it has been refreshed using the entity manager. I can re populate the persistent entity with the first new instance I created. I now have the persistent entity and the original entity before any changes I made.

Entity copy code:

public Object getOriginalEntity(Object persistentEntity) throws Exception {
 Object current = persistentEntity.getClass().newInstance();
 Object original = persistentEntity.getClass().newInstance();

 this.copyEntity(persistentEntity, current);
 this.em.refresh(persistentEntity);
 this.copyEntity(persistentEntity, original);
 this.copyEntity(current, persistentEntity);

 return original;
}

private void copyEntity(Object getEntity, Object setEntity) {
 Class entityClass = getEntity.getClass();

 try {
 Method[] methods = entityClass.getMethods();

 for (Method method : methods) {
 if (method.getReturnType() != Void.class &&
 !method.isAnnotationPresent(Transient.class)) {

 Method setMethod;

 try {
 setMethod = entityClass.getMethod(
 "set" + method.getName().substring(3),
 method.getReturnType()
 );

 setMethod.invoke(setEntity, method.invoke(getEntity));
 } catch(NoSuchMethodException nsme) {
 /* Ignore this for now. */
 }
 }
 }
 } catch (Exception e) {
 e.printStackTrace();
 }
}

I don't think it is possible to use @AroundInvoke within an entity. I started to write an AOP interceptor which can intercept all set methods for a class annotated with @Entity. This would allow me to do something similar to your example. However I think that this would have a bigger overhead than copying the values from the entity at update time as the map would automatically be populated at load time.

I think I will write a base entity listener, that copies the entities values into a map, refreshes the entity, copies the refreshed values into a map, and replaces the original values. I only have to do this if I need to determine whether a value has changed or not.

Thanks for your ideas.