JPA是否为每个请求创建实体管理器工厂？

Question

First of all I am new to JPA and Jax-rs, i am trying to develop a rest service. So i have created a resource class and annotated it.

@Path("/companies")
public class CompanyResource {

private EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("test");

@GET
@Produces({MediaType.APPLICATION_JSON})
public List<Company> getCompanies() {
    EntityManager entityManager = entityManagerFactory.createEntityManager();

    return new ArrayList<>();
}

@GET
@Path("{companyId}")
@Produces({MediaType.APPLICATION_JSON})
public Company getCompany(@PathParam("companyId") int id) {

    return new Company();
}
}

From what i have understood about jax-rs for every client request instance of CompanyResource will be created, that means every time new EntityManagerFactory will be created, which i guess is not a good idea, as i just need it to create entity managers, which could be done with only one instance of it. So what is a proper way to achieve this? Or is it ok to create new instance of this factory for every request?

PS i have seen some examples where they use @Stateless annotation and inject Entity Manager, but i guess they use EJB there(i might be wrong) and i don't want to deep into EJB right now.

Answer 1

I think you should inject the entitymanager itself (not the factory), and let the container take care of instantiation and scopes. What we usually do is something like

@Stateless
@Path("services")
public class MyServices {

  @PersistenceContext
  private EntityManager em;

// ... 

apart from the @Stateless (which imho you should use, there's no need to get deep into EJB for this), it's actually quite simple.