Why shouldn't I use a JSF SessionScoped bean for logic?

Question

I\'m developing a java EE web app using JSF with a shopping cart style process, so I want to collect user input over a number of pages and then do something with it.

Answer 1

Why is it called a session bean, as far as I can see it has nothing to do with a session, I could achieve the same by storing a pojo in a session.

From the old J2EE 1.3 tutorial:

What Is a Session Bean?

A session bean represents a single client inside the J2EE server. To access an application that is deployed on the server, the client invokes the session bean's methods. The session bean performs work for its client, shielding the client from complexity by executing business tasks inside the server.

As its name suggests, a session bean is similar to an interactive session. A session bean is not shared--it may have just one client, in the same way that an interactive session may have just one user. Like an interactive session, a session bean is not persistent. (That is, its data is not saved to a database.) When the client terminates, its session bean appears to terminate and is no longer associated with the client.

So it has to do with a "session". But session not necessarily means "HTTP session"

What's the point of being able to inject it, if all I'm gonna be injecting' is a new instance of this SFSB then I might as well use a pojo?

Well, first of all, you don't inject a SFSB in stateless component (injection in another SFSB would be ok), you have to do a lookup. Secondly, choosing between HTTP session and SFSB really depends on your application and your needs. From a pure theoretical point of view, the HTTP session should be used for presentation logic state (e.g. where you are in your multi page form) while the SFSB should be used for business logic state. This is nicely explained in the "old" HttpSession v.s. Stateful session beans thread on TSS which also has a nice example where SFSB would make sense:

You may want to use a stateful session bean to track the state of a particular transaction. i.e some one buying a railway ticket.

The web Session tracks the state of where the user is in the html page flow. However, if the user then gained access to the system through a different channel e.g a wap phone, or through a call centre you would still want to know the state of the ticket buying transaction.

But SFSB are not simple and if you don't have needs justifying their use, my practical advice would be to stick with the HTTP session (especially if all this is new to you). Just in case, see:

• Stateless and Stateful Enterprise Java Beans
• Stateful EJBs in web application?

So back to the main issue I see written all over that JSF is a presentation technology, so it should not be used for logic, but it seems the perfect option for collecting user input.

That's not business logic, that's presentation logic.

So I have multiple tiers (...)

No. You have probably a client tier, a presentation tier, a business tier, a data tier. What you're describing looks more like layers (not even sure). See:

• Can anybody explain these words: Presentation Tier, Business Tier, Integration Tier in java EE with example?
• Spring, Hibernate, Java EE in the 3 Tier architecture

Why is this so bad?

I don't know, I don't know what you're talking about :) But you should probably just gather the multi page form information into a SessionScoped bean and call a Stateless Session Bean (SLSB) at the end of the process.