Single DAO & generic CRUD methods (JPA/Hibernate + Spring)

Question

Following my previous question, DAO and Service layers (JPA/Hibernate + Spring), I decided to use just a single DAO for my data layer (at least at the beginning) in an application using JPA/Hibernate, Spring and Wicket. The use of generic CRUD methods was proposed, but I'm not very sure how to implement this using JPA. Could you please give me an example or share a link regarding this?

Answer 1

Here is an example interface:

public interface GenericDao<T, PK extends Serializable> {     T create(T t);     T read(PK id);     T update(T t);     void delete(T t); } 

And an implementation:

public class GenericDaoJpaImpl<T, PK extends Serializable>      implements GenericDao<T, PK> {      protected Class<T> entityClass;      @PersistenceContext     protected EntityManager entityManager;      public GenericDaoJpaImpl() {         ParameterizedType genericSuperclass = (ParameterizedType) getClass()              .getGenericSuperclass();         this.entityClass = (Class<T>) genericSuperclass              .getActualTypeArguments()[0];     }      @Override     public T create(T t) {         this.entityManager.persist(t);         return t;     }      @Override     public T read(PK id) {         return this.entityManager.find(entityClass, id);     }      @Override     public T update(T t) {         return this.entityManager.merge(t);     }      @Override     public void delete(T t) {         t = this.entityManager.merge(t);         this.entityManager.remove(t);     } }