Java - Object parameter in method must have @Entity annotation

Question

I want to create a remote EJB for an entity class. Is there a way of implementing a method with one parameter beign an object of a class that specifically has the @Entity annotation? The purpose of this, is to create just one bean for all my entities.

Example:

public void save(Entity ent){
     em.persist(ent);
}

Answer 1

If you just have 1 ejb for all entities you will soon run into problems when you have to handle some of them in a special way.

But you can do like this with an abstract super-ejb, and still have 1 ejb per entity, but its very easy to create. And you can still overwrite the default, inherited methods.

public abstract class AbstractEjb<T> {
    private Class<T> entityClass;

    public AbstractEjb(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();
    }

}

To implement for an entity just do

@Stateless
public class TestEjb extends AbstractEjb<TestEntity> {

    @PersistenceContext(unitName = "...")
    private EntityManager em;

    public TestEjb() {
        super(TestEntity.class);
    }

    public EntityManager getEntityManager() {
        return em;
    }
}

Source: Generate JSF pages from entity classes in Netbeans.