What are the advantages of using spring in a web app with struts 2 and hibernate.

At the moment I have a web app which uses struts 2 . The struts 2 actions create an instance of the dao and the struts form objects are also hibernate persistence objects and they simply get passed from the action to the dao and are then persisted to the DB by the DAO.

My question is what would be the advantages if any of adding another layer to my webapp where a spring service is created by the struts 2 actions and then the spring service creates the dao and passes the form object to the dao.

Thanks in advance

Spunog