How to achieve “not in” by using Restrictions and criteria in Hibernate?

Your question is somewhat unclear. Assuming “Category” is a root entity and “2,3” are ids (or values of some property of the category”) you can exclude them using the following:

Criteria criteria = ...; // obtain criteria from somewhere, like session.createCriteria() 
criteria.add(
  Restrictions.not(
     // replace "id" below with property name, depending on what you're filtering against
    Restrictions.in("id", new long[] {2, 3})
  )
);

Same can be done with DetachedCriteria.