JSF Controller, Service and DAO

37
votes

I'm trying to get used to how JSF works with regards to accessing data (coming from a spring background)

I'm creating a simple example that maintains a list of users, I have something like

<h:dataTable value="#{userListController.userList}" var="u">
    <h:column>#{u.userId}</h:column>
    <h:column>#{u.userName}</h:column>
</h:dataTable>

Then the "controller" has something like

@Named(value = "userListController")
@SessionScoped
public class UserListController {
    @EJB
    private UserListService userListService;

    private List<User> userList;

    public List<User> getUserList() {
        userList = userListService.getUsers();
        return userList;
    }
}

And the "service" (although it seems more like a DAO) has

public class UserListService {

    @PersistenceContext
    private EntityManager em;

    public List<User> getUsers() {
        Query query = em.createQuery("SELECT u from User as u");
        return query.getResultList();
    }
}

Is this the correct way of doing things? Is my terminology right? The "service" feels more like a DAO? And the controller feels like it's doing some of the job of the service.

2
jsfjakarta-eejpaejbdao

2 Answers

76
votes

Is this the correct way of doing things?

Apart from performing business logic the inefficient way in a managed bean getter method, and using a too broad managed bean scope, it looks okay. If you move the service call from the getter method to a @PostConstruct method and use either @RequestScoped or @ViewScoped instead of @SessionScoped, it will look better.

See also:

Is my terminology right?

It's okay. As long as you're consistent with it and the code is readable in a sensible way. Only your way of naming classes and variables is somewhat awkward (illogical and/or duplication). For instance, I personally would use users instead of userList, and use var="user" instead of var="u", and use id and name instead of userId and userName. Also, a "UserListService" sounds like it can only deal with lists of users instead of users in general. I'd rather use "UserService" so you can also use it for creating, updating and deleting users.

See also:

The "service" feels more like a DAO?

It isn't exactly a DAO. Basically, JPA is the real DAO here. Previously, when JPA didn't exist, everyone homegrew DAO interfaces so that the service methods can keep using them even when the underlying implementation ("plain old" JDBC, or "good old" Hibernate, etc) changes. The real task of a service method is transparently managing transactions. This isn't the responsibility of the DAO.

See also:

And the controller feels like it's doing some of the job of the service.

I can imagine that it does that in this relatively simple setup. However, the controller is in fact part of the frontend not the backend. The service is part of the backend which should be designed in such way that it's reusable across all different frontends, such as JSF, JAX-RS, "plain" JSP+Servlet, even Swing, etc. Moreover, the frontend-specific controller (also called "backing bean" or "presenter") allows you to deal in a frontend-specific way with success and/or exceptional outcomes, such as in JSF's case displaying a faces message in case of an exception thrown from a service.

See also:

All in all, the correct approach would be like below:

<h:dataTable value="#{userBacking.users}" var="user">
    <h:column>#{user.id}</h:column>
    <h:column>#{user.name}</h:column>
</h:dataTable>

@Named
@RequestScoped // Use @ViewScoped once you bring in ajax (e.g. CRUD)
public class UserBacking {

    private List<User> users;

    @EJB
    private UserService userService;

    @PostConstruct
    public void init() {
        users = userService.listAll();
    }

    public List<User> getUsers() {
        return users;
    }

}

@Stateless
public class UserService {

    @PersistenceContext
    private EntityManager em;

    public List<User> listAll() {
        return em.createQuery("SELECT u FROM User u", User.class).getResultList();
    }

}

You can find here a real world kickoff project here utilizing the canonical Java EE / JSF / CDI / EJB / JPA practices: Java EE kickoff app.

See also:

7
votes

It is a DAO, well actually a repository but don't worry about that difference too much, as it is accessing the database using the persistence context.

You should create a Service class, that wraps that method and is where the transactions are invoked.

Sometimes the service classes feel unnecessary, but when you have a service method that calls many DAO methods, their use is more warranted.

I normally end up just creating the service, even if it does feel unnecessary, to ensure the patterns stay the same and the DAO is never injected directly.

This adds an extra layer of abstraction making future refactoring more flexible.