Hiberate save-update listener and ascertaining field changes

Question

Good day.

I've implemented a Hibernate save-update listener by extending org.hibernate.event.def.DefaultSaveOrUpdateEventListener.DefaultSaveOrUpdateEventListener and overriding onSaveOrUpdate(SaveOrUpdateEvent e).

@Override
public void onSaveOrUpdate(SaveOrUpdateEvent evt) throws HibernateException {
    super.onSaveOrUpdate(evt);
    Object entity = evt.getEntity();
    if (entity instanceof Tag) {
        updateIndex((Tag) entity);
    }
}

My challenge is that I only want to execute the updateIndex(((Tag) entity) method if certain fields in the Tag instance have changed.

Is there a way determine which fields induced the save or update such that I can decide whether to do further processing or not?

Thank you.