How to reuse a Criteria object with hibernate?

Criteria.setProjection(null);
Criteria.setResultTransformer(Criteria.ROOT_ENTITY);

Will effectively "reset" the criteria between the rowCount projection and execution of the criteria itself.

I would make sure your Order hasn't been added before doing the rowCount, it'll slow things down. My implementation of PaginatedList ALWAYS runs a count query before looking for results, so ordering isn't an issue.

well, DetachedCriteria are Serializable, so you have built-in (if inelegant) deep clone support. You could serialize the initial criteria to a byte[] once on construction, then deserialize it each time you want to use it.