Proper use of backing beans

Question

Yes, I searched for questions about backing beans and I found many questions. I read them, and I get some parts of it but I need to ask another question, sorry.

After what I understand backing beans are needed because of JSF MVC pattern. Backing beans are the model. So if you have a page that displays a form, an image and a login box the backing beans will have getter/setter pairs for the data that needs to be exposed or changed in the view. And the backing beans will also have methods related to this such as what happen when you submit the form, login in etc.

So my question is if the statements above is correct, and the number of backing beans you make for the components above is dependent on how much code it is?

Would one backing bean exposing methods and getter/setter pairs for all components on this page be legal and "correct" (meaning that I don't do any wrong) in the same way as making 3 backing beans; one for each component would also be fine.

Does it all boil down to experience to see when you should separate vs. making one backing bean for each page, and also the logical part of it? I heard one guy made a backing bean for each component on the page but it sounds like you end up with a lot of small classes.

I would highly apprciate if somebody could verify and correct me.

Answer 1

It is legal for all components in a view to be bound to one managed bean for properties and actions. IDE tooling may encourage you to do this with a single backing bean.

From a class point of view however this approach lacks granularity and can make the managed beans difficult to test. If a class doesn't have a clearly defined purpose then it can be difficult to assert they are doing that job. See warning sign "Summing up what the class does includes the word “and”". All versions of JSF support dependency injection so it is relatively easy to rely on composition to assemble your managed beans.

This is a somewhat subjective topic and the answer depends on other factors (application scale; view design; page function.)