JSF Controller, Service and DAO

jsf jakarta-ee jpa ejb dao

31,052

Solution 1

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.

Solution 2

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.

31,052

Author by

PDStat

Updated on July 16, 2022

Comments

PDStat almost 2 years

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.

PDStat almost 9 years

thanks, I'll probably just add that extra layer then. From a JSF perspective does what I'm doing look like the correct way to go?
NimChimpsky almost 9 years

Looks fine, does it have to be session scoped - using sessions makes clustering somewhat more complex (but also commonly used). Not used jsf myself, I prefer anglular, vanilla html, and a rest api.
PDStat almost 9 years

I'll be adding in some result pages saying things like 'user x added' or 'user x removed' so I assume so, not really sure yet just playing.
Tiny almost 9 years

"JPA is the real DAO here" gives my brain a deep impact to understand this statement. :) Is it anything that provides an abstraction to some kind of persistence mechanism like a DB and allows retrieval and persistence of domain objects to and from the DB without exposing the internal details of the underlying DB is said to be a DAO? This is somewhat confusing as compared to older questions/answers/blogs/tutorials/articles somewhere else.
BalusC almost 9 years

@Tiny: perhaps this answer is helpful to understand the original intent behind DAO pattern: stackoverflow.com/questions/7070467/dao-and-jdbc-relation
LyK over 8 years

@BalusC Why is Session Scope too broad? By using the view scope the list will have to be build every time the user loads the page, right? Isn't that "bad"? Or is it that we just prefer that, more than keeping the bean alive for the whole session and consuming memory?
BalusC over 8 years

@LyK: click "How to choose the right bean scope?" for explanation.
LyK over 8 years

@BalusC Yes, I have read that. But I initially thought that in this case session scope would be more appropriate. I guess we prefer to query the db again rather than keeping the results in memory for the whole session. Ty!
BalusC over 8 years

@LyK: You shouldn't cache DB results in all sessions in the frontend. You should cache them in a single place in the backend. JPA offers 2nd level cache possibility. Additional advantage, it knows precisely when to invalidate a cached entity.
developer10 over 7 years

@BalusC I'm having issues trying to implement this wiring in my own example. @PostConstruct public void init() method is giving me error: WELD-000049: Unable to invoke public void com.example.jsf.GradBacking.init() on com.example.jsf.GradBacking@8dbd4b Also, is there any difference between using javax.faces.bean.RequestScoped and javax.enterprise.context.RequestScoped Does anything about this issue comes to your mind? Thank you!
BalusC over 7 years

@developer10: That method just threw an exception. When getting an exception, always look at bottommost root cause in stack trace for the root cause the problem. All causes there above are just consequences of each other.
developer10 over 7 years

@BalusC Thank you, will take a look at the stack now. Btw, there's another part of the Q regarding the two types of RequestScoped annotation - does the choice thereof matter in this case? And finally -- I forgot to mention that when the init() method is in place, none of my EL expressions are evaluated in the JSF (it this due to the exception being thrown??) (I have a dummy field to test), and if I comment it out, then they are evaluated.
Serg Shapoval about 7 years

You saved my life! thanx