It seems that the Dao implementation of the article is written to be used in a
dependency injection environment such as a Spring context or a Java EE server
where the container will manage setting the entityManager field when it sees
that it is annotated with @PersistenceContext (provided you have set up the
container correctly).
When you instantiate a new Dao implementation yourself the entityManager field
will still have its default value of null.
If you do not use a dependency injection container you have to create the
entityManager yourself using something like:
EntityManagerFactory emf = Persistence.createEntityManagerFactory("myPU");
EntityManager em = emf. createEntityManager();
Where "myPU" is the persistence unit name as defined in persistence.xml.
hth,
Henno
-----Oorspronkelijk bericht-----
Van: aitor [mailto:[email protected]]
Verzonden: vrijdag 5 april 2013 13:21
Aan: [email protected]
Onderwerp: my fist openjpa porject / problem. help me please
hello
i an tring to build my firts openjpa app
i am reading this article
(http://java.dzone.com/articles/jpa-implementation-patterns) and building it
for this i make this:
1.- generic interface:
public interface IGenericDao<K, E> {
void persist(E entity);
}
2.- other interface, my interface.
public interface IWsSrvTrackRequest extends IGenericDao<Integer,
Wssrvtrackrequest>{
void wsSrvRequestPersist(Wssrvtrackrequest request);
}
3.- generic JPA-DAO:
public abstract class JpaDao<K, E> implements IGenericDao<K, E> {
protected Class<E> entityClass;
@PersistenceContext
protected EntityManager entityManager;
public JpaDao() {
ParameterizedType genericSuperclass = (ParameterizedType)
getClass().getGenericSuperclass();
this.entityClass = (Class<E>)
genericSuperclass.getActualTypeArguments()[1];
}
public void persist(E entity) {
entityManager.persist(entity);
}
}
}
4.- my jpa-dao implementation (the Wssrvtrackrequest obj is one jpa object
(entity)).
public class JpaWsSrvTrackRequestDaoImpl extends JpaDao<Integer,
Wssrvtrackrequest> implements IWsSrvTrackRequest {
public void wsSrvRequestPersist(Wssrvtrackrequest request){
entityManager.persist(request);//this is the error line JpaDao.java:20
}
}
i am make one *main *class:
public static void main(String[] args) {
IWsSrvTrackRequest r = new JpaWsSrvTrackRequestDaoImpl();
Wssrvtrackrequest v = new Wssrvtrackrequest();
v.setWssrvreqIp("la ip");
v.setWssrvreqOid("oid");
v.setWssrvreqOiduser("oiduser");
v.setWssrvreqRequest("la request");
r.persist(v);
}
but it always returns one nullpointerexception.
Exception in thread "main" java.lang.NullPointerException
at com.myclass.db.dao.JpaDao.persist(JpaDao.java:20)
at com.myclass.db.dao.ll.main(ll.java:20)
Is posible use this from one main class or only into one application
server?
Can you help me please?
thanks
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