如何使用JPA和Facade

Question

我对JPA和Facade modell有问题，因为我现在不知道如何使用它。我有一个班叫"Kandidatenstam"（这是一种天赋）。对于这个Kandidatenstam，存在一个门面和控制器。还有一个抽象立面和一个抽象控制器。那么，我必须在bean中做什么呢？例如，从id为4的数据库中获取对象？

这是我的代码

抽象立面

public abstract class AbstractFacade<T> {
private Class<T> entityClass;
public AbstractFacade(Class<T> entityClass) {
    this.entityClass = entityClass;
}
protected abstract EntityManager getEntityManager();
public void create(T entity) {
    getEntityManager().persist(entity);
}
public void edit(T entity) {
    getEntityManager().merge(entity);
}
public void remove(T entity) {
    getEntityManager().remove(getEntityManager().merge(entity));
}
public T find(Object id) {
    return getEntityManager().find(entityClass, id);
}
public List<T> findAll() {
    javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
    cq.select(cq.from(entityClass));
    return getEntityManager().createQuery(cq).getResultList();
}
public List<T> findRange(int[] range) {
    javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
    cq.select(cq.from(entityClass));
    javax.persistence.Query q = getEntityManager().createQuery(cq);
    q.setMaxResults(range[1] - range[0] + 1);
    q.setFirstResult(range[0]);
    return q.getResultList();
}
public int count() {
    javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
    javax.persistence.criteria.Root<T> rt = cq.from(entityClass);
    cq.select(getEntityManager().getCriteriaBuilder().count(rt));
    javax.persistence.Query q = getEntityManager().createQuery(cq);
    return ((Long) q.getSingleResult()).intValue();
}
}

Kandidatenstamm立面

 @Stateless
public class KandidatenstammFacade extends AbstractFacade<Kandidatenstamm> {
@PersistenceContext(unitName = "ffswebadministrationPU")
private EntityManager em;
@Override
protected EntityManager getEntityManager() {
    return em;
}
public KandidatenstammFacade() {
    super(Kandidatenstamm.class);
}
}

Answer 1

好吧，我自己搞定了。只进行EJB注入并使用Facade。这里的例子是"Personenstamm"（原则上与"Kandidatenstam"相同）

@EJB
private PersonenstammFacade personenstammFacade;
....
List <Personenstamm> personlist;
personlist = personenstammFacade.findAll();
....
//do what you want with this list