Simplyfing the DAO layer with Spring and Java Generics - the Abstract JPA DAO

AbstractJpaDAO.java

public abstract class AbstractJpaDAO< T extends Serializable > {
   
   private Class< T > clazz;
   
   @PersistenceContext
   EntityManager entityManager;
   
   public void setClazz( final Class< T > clazzToSet ){
      this.clazz = clazzToSet;
   }
   
   public T findOne( final Long id ){
      return entityManager.find( clazz, id );
   }
   public List< T > findAll(){
      return entityManager.createQuery( "from " + clazz.getName() )
       .getResultList();
   }
   
   public void save( final T entity ){
      entityManager.persist( entity );
   }
   
   public void update( final T entity ){
      entityManager.merge( entity );
   }
   
   public void delete( final T entity ){
      entityManager.remove( entity );
   }
   public void deleteById( final Long entityId ){
      final T entity = getById( entityId );
      
      delete( entity );
   }
}

This gist is used in:
http://www.baeldung.com/2011/12/13/the-persistence-layer-with-spring-3-1-and-jpa/

This gist is also used in:
http://www.baeldung.com/2011/12/08/simplifying-the-data-access-layer-with-spring-and-java-generics/