Write Less DAOs with Spring Hibernate using Annotations

Question

My Spring+Hibernate configuration files are small and super tight. I use auto scanning to find my model entities/daos.

I don't want to have to write a DAO + DAOImpl for EVERY Entity in my hierarchy.

Some may qualify to have their own, like if they have complex relationships with other entities and require more than basic CRUD functionality. But for the rest...

Is there any way to circumvent the defacto standard?

Say, something like a generic DAO, ex:

http://www.ibm.com/developerworks/java/library/j-genericdao/index.html

Then I can do something like

  GenericDao dao = appContext.getBean("genericDao");
  dao.save(car);            
  dao.save(lease);

Is this possible with annotations? I don't want to have to configure anything in xml. If I cannot do above, is it still possible to have one GenericDaoImpl.java with something like:

 @Repository("carDao")
 @Repository("leaseDao")
 class GenericDaoImpl extends CustomHibernateDaoSupport implements GenericDao {
 ...
 }

and then

  GenericDao dao = appContext.getBean("carDao");
  dao.save(car);            
  dao = appContext.getBean("leaseDao"); //carDao is garbage coll.
  dao.save(lease);

Is this practical at all?

Answer 1

Using generics, you might try something like this:

@Repository
@Transactional
public class GenericDAOImpl<T> implements GenericDAO<T> {

    @Autowired
    private SessionFactory factory;

    public void persist(T entity) {
        Session session = factory.getCurrentSession();
        session.persist(entity);
    }

    @SuppressWarnings("unchecked")
    public T merge(T entity) {
        Session session = factory.getCurrentSession();
        return (T) session.merge(entity);
    }

    public void saveOrUpdate(T entity) {
        Session session = factory.getCurrentSession();
        session.saveOrUpdate(entity);
    }

    public void delete(T entity) {
        Session session = factory.getCurrentSession();
        session.delete(entity);
    }

}

The content may be different, but the general idea is applicable.

You should be able to then autowire the DAO in your controller and service classes by using

@Autowired
private GenericDAO<Car> carDao;

Answer 2

You can combine Spring/Hibernate with JPA, which provides the EntityManager for a large amount of basic persistence tasks:

@Service
public class CarService {

    @PersistenceContext
    private EntityManager em;

    public void saveCarAndLease(Car car, Lease lease) {
        em.persist(car);
        em.persist(lease);
    }
}

It will also handle transactions and simple queries without needing to write a DAO. For the more complex operations, you can still write a DAO and fall back to Hibernate's SessionFactory (although JPA is an option here too).

Some tutorials suggest you should still write the DAO for abstraction of the JPA plumbing. However, I have personally found this unnecessary (JPA has a very small integration footprint), and in fact this is also the way Spring Roo deals with the data layer behind the scenes.

Answer 3

Have you tried to use Spring Data. I mean to say Spring JPA where you can use repositories.
You can eliminate writing all stuffs for each entity.