The basic programming model for templating looks as follows, for methods that can be part of any custom data access object or business service. There are no restrictions on the implementation of the surrounding object at all, it just needs to provide a Hibernate SessionFactory. It can get the latter from anywhere, but preferably as bean reference from a Spring IoC container - via a simple setSessionFactory(..) bean property setter. The following snippets show a DAO definition in a Spring container, referencing the above defined SessionFactory, and an example for a DAO method implementation.

<beans>

  <bean id="myProductDao" class="product.ProductDaoImpl">
    <property name="sessionFactory" ref="mySessionFactory"/>
  </bean>

</beans>

public class ProductDaoImpl implements ProductDao {

    private HibernateTemplate hibernateTemplate;

    public void setSessionFactory(SessionFactory sessionFactory) {
        this.hibernateTemplate = new HibernateTemplate(sessionFactory);
    }

    public Collection loadProductsByCategory(String category) throws DataAccessException {
        return this.hibernateTemplate.find("from test.Product product where product.category=?", category);
    }
}

The HibernateTemplate class provides many methods that mirror the methods exposed on the Hibernate Session interface, in addition to a number of convenience methods such as the one shown above. If you need access to the Session to invoke methods that are not exposed on the HibernateTemplate, you can always drop down to a callback-based approach like so.

public class ProductDaoImpl implements ProductDao {

    private HibernateTemplate hibernateTemplate;

    public void setSessionFactory(SessionFactory sessionFactory) {
        this.hibernateTemplate = new HibernateTemplate(sessionFactory);
    }

    public Collection loadProductsByCategory(final String category) throws DataAccessException {
        return this.hibernateTemplate.execute(new HibernateCallback() {

            public Object doInHibernate(Session session) {
                Criteria criteria = session.createCriteria(Product.class);
                criteria.add(Expression.eq("category", category));
                criteria.setMaxResults(6);
                return criteria.list();
            }
        };
    }
}

A callback implementation effectively can be used for any Hibernate data access. HibernateTemplate will ensure that Session instances are properly opened and closed, and automatically participate in transactions. The template instances are thread-safe and reusable, they can thus be kept as instance variables of the surrounding class. For simple single step actions like a single find, load, saveOrUpdate, or delete call, HibernateTemplate offers alternative convenience methods that can replace such one line callback implementations. Furthermore, Spring provides a convenient HibernateDaoSupport base class that provides a setSessionFactory(..) method for receiving a SessionFactory, and getSessionFactory() and getHibernateTemplate()for use by subclasses. In combination, this allows for very simple DAO implementations for typical requirements:

public class ProductDaoImpl extends HibernateDaoSupport implements ProductDao {

    public Collection loadProductsByCategory(String category) throws DataAccessException {
        return this.getHibernateTemplate().find(
            "from test.Product product where product.category=?", category);
    }
}

As alternative to using Spring's HibernateTemplate to implement DAOs, data access code can also be written in a more traditional fashion, without wrapping the Hibernate access code in a callback, while still respecting and participating in Spring's generic DataAccessException hierarchy. The HibernateDaoSupport base class offers methods to access the current transactional Session and to convert exceptions in such a scenario; similar methods are also available as static helpers on the SessionFactoryUtils class. Note that such code will usually pass 'false' as the value of the getSession(..) methods 'allowCreate' argument, to enforce running within a transaction (which avoids the need to close the returned Session, as its lifecycle is managed by the transaction).

public class HibernateProductDao extends HibernateDaoSupport implements ProductDao {

    public Collection loadProductsByCategory(String category) throws DataAccessException, MyException {
        Session session = getSession(false);
        try {
            Query query = session.createQuery("from test.Product product where product.category=?");
            query.setString(0, category);
            List result = query.list();
            if (result == null) {
                throw new MyException("No search results.");
            }
            return result;
        }
        catch (HibernateException ex) {
            throw convertHibernateAccessException(ex);
        }
    }
}

The advantage of such direct Hibernate access code is that it allows any checked application exception to be thrown within the data access code; contrast this to the HibernateTemplate class which is restricted to throwing only unchecked exceptions within the callback. Note that you can often defer the corresponding checks and the throwing of application exceptions to after the callback, which still allows working with HibernateTemplate. In general, the HibernateTemplate class' convenience methods are simpler and more convenient for many scenarios.

Each JDO-based DAO will then receive the PersistenceManagerFactory through dependency injection. Such a DAO could be coded against plain JDO API, working with the given PersistenceManagerFactory, but will usually rather be used with the Spring Framework's JdoTemplate:

<beans>

  <bean id="myProductDao" class="product.ProductDaoImpl">
    <property name="persistenceManagerFactory" ref="myPmf"/>
  </bean>

</beans>

public class ProductDaoImpl implements ProductDao {

    private JdoTemplate jdoTemplate;

    public void setPersistenceManagerFactory(PersistenceManagerFactory pmf) {
        this.jdoTemplate = new JdoTemplate(pmf);
    }

    public Collection loadProductsByCategory(final String category) throws DataAccessException {
        return (Collection) this.jdoTemplate.execute(new JdoCallback() {
            public Object doInJdo(PersistenceManager pm) throws JDOException {
                Query query = pm.newQuery(Product.class, "category = pCategory");
                query.declareParameters("String pCategory");
                List result = query.execute(category);
                // do some further stuff with the result list
                return result;
            }
        });
    }
}

A callback implementation can effectively be used for any JDO data access. JdoTemplate will ensure that PersistenceManagers are properly opened and closed, and automatically participate in transactions. The template instances are thread-safe and reusable, they can thus be kept as instance variables of the surrounding class. For simple single-step actions such as a single find, load, makePersistent, or delete call, JdoTemplate offers alternative convenience methods that can replace such one line callback implementations. Furthermore, Spring provides a convenient JdoDaoSupport base class that provides a setPersistenceManagerFactory(..) method for receiving a PersistenceManagerFactory, and getPersistenceManagerFactory() and getJdoTemplate() for use by subclasses. In combination, this allows for very simple DAO implementations for typical requirements:

public class ProductDaoImpl extends JdoDaoSupport implements ProductDao {

    public Collection loadProductsByCategory(String category) throws DataAccessException {
        return getJdoTemplate().find(
            Product.class, "category = pCategory", "String category", new Object[] {category});
    }
}

As alternative to working with Spring's JdoTemplate, you can also code Spring-based DAOs at the JDO API level, explicitly opening and closing a PersistenceManager. As elaborated in the corresponding Hibernate section, the main advantage of this approach is that your data access code is able to throw checked exceptions. JdoDaoSupport offers a variety of support methods for this scenario, for fetching and releasing a transactional PersistenceManager as well as for converting exceptions.

Each JPA-based DAO will then receive a EntityManagerFactory via dependency injection. Such a DAO can be coded against plain JPA and work with the given EntityManagerFactory or through Spring's JpaTemplate:

<beans>

  <bean id="myProductDao" class="product.ProductDaoImpl">
    <property name="entityManagerFactory" ref="myEmf"/>
  </bean>

</beans>

public class JpaProductDao implements ProductDao {

    private JpaTemplate jpaTemplate;

    public void setEntityManagerFactory(EntityManagerFactory emf) {
        this.jpaTemplate = new JpaTemplate(emf);
    }

    public Collection loadProductsByCategory(final String category) throws DataAccessException {
        return (Collection) this.jpaTemplate.execute(new JpaCallback() {
            public Object doInJpa(EntityManager em) throws PersistenceException {
                Query query = em.createQuery("from Product as p where p.category = :category");
                query.setParameter("category", category);
                List result = query.getResultList();
                // do some further processing with the result list
                return result;
            }
        });
    }
}

The JpaCallback implementation allows any type of JPA data access. The JpaTemplate will ensure that EntityManagers are properly opened and closed and automatically participate in transactions. Moreover, the JpaTemplate properly handles exceptions, making sure resources are cleaned up and the appropriate transactions rolled back. The template instances are thread-safe and reusable and they can be kept as instance variable of the enclosing class. Note that JpaTemplate offers single-step actions such as find, load, merge, etc along with alternative convenience methods that can replace one line callback implementations.

Furthermore, Spring provides a convenient JpaDaoSupport base class that provides the get/setEntityManagerFactory and getJpaTemplate() to be used by subclasses:

public class ProductDaoImpl extends JpaDaoSupport implements ProductDao {

    public Collection loadProductsByCategory(String category) throws DataAccessException {
        Map<String, String> params = new HashMap<String, String>();
        params.put("category", category);
        return getJpaTemplate().findByNamedParams("from Product as p where p.category = :category", params);
    }
}

Besides working with Spring's JpaTemplate, one can also code Spring-based DAOs against the JPA, doing one's own explicit EntityManager handling. As also elaborated in the corresponding Hibernate section, the main advantage of this approach is that your data access code is able to throw checked exceptions. JpaDaoSupport offers a variety of support methods for this scenario, for retrieving and releasing a transaction EntityManager, as well as for converting exceptions.

JpaTemplate mainly exists as a sibling of JdoTemplate and HibernateTemplate, offering the same style for people used to it.