I have done a small experiment with #FlowScoped beans, whose purpose, as I understand, is to make easier creating "wizard-type" web applications, gradually accumulating data over a sequence of pages, then, once all the data is ready, writing it to the persistent storage (this is just an example, nothing prevents of course to write to the persistent storage during intermediate steps). As I saw, the calls to a #FlowScoped bean are not synchronized, and thus there is in principle the possibility of corrupting the data stored in the bean (by doing a double submit, or launching by any other means two almost simultaneous HTTP requests, which invoke the methods of the bean). This unlike #ConversationScoped beans the calls to which are synchronized.
What puzzles me is that about #SessionScoped beans I have found several links which speak about the need to synchronize the access to a #SessionScoped bean (or recommending not to use them at all, apart from user data which changes rarely), but I have not found anything like that about #FlowScoped beans.
What is considered then to be a "best practice" for using #FlowScoped beans? Am I missing something?
EDIT
#FlowScoped seems, at least to me, to be motivated in part by Spring WebFlow, with which I have some experience, and which, as I know, offers integration with JSF 2 (not all JSF 2.2 features seem to be implemented, but it seems that PrimeFaces is usable, for example). I know that Spring WebFlow + JSF is actually used in "real world" applications, and the issue of thread safety of flow scoped objects is handled there elegantly together with double submit issues (flow execution id must be supplied with each HTTP request, and it expires and a new one is returned after a HTTP request which invokes a Spring WebFlow "action" method: therefore one cannot invoke concurrently more than one "action" method for the same user and flow id).
So I want to understand, what is the best practice in the case of JSF 2.2 if I wish to use the #FlowScoped beans to construct an application "flow" (without using Spring WebFlow). Do I really need to synchronize the access to #FlowScoped beans myself, or there is some standard way to deal with such issues?
I have a #ManagedBean #SessionScoped class to represent a user session. Assume it has a theoretical method doHorribleThings(). Access to methods of this bean through JSF can, for example, be enabled through Expression Language attributes such as action="#{userSession.doHorribleThings()}" on a Prime Faces p:commandButton.
My question is, does JSF manage access security for such method? Can a user issue performing the action of a button that is not being rendered for him, e.g. by sending an artificial HTTP package? Or does JSF capsulate a virtual client desktop that stretches accross the network, effectively enabling access control through GUI design?
No, JSF doesn't have an access security for invoking a method in a managedbean other than the UI, as far as I know.
Because if your able to mimic an action that happens through the click of a JSP/Primefaces button with a manual HTTP request then JSF container cannot identify the difference between the two and hence work the same way for both the request
I would like to access a view scope managed bean inside a Servlet.
I searched for similar question and got these ones:
how to get beans from view scope which uses FacesContext.getCurrentInstance(), inapplicable inside a Servlet because it should give a null result
JSF - get managed bean by name which treats all other scopes but not viewscope
I'm going to think it is not possible, is it ?
There is the simple solution to change that bean scope to session scope but it is a last chance because I'm worried by memory consumption.
My final need is the following: the managebean contains some data displayed in a dataTable. The same page should include the image (mandatory) of chart representation of those data. The image can be produced by a Servlet but it needs to access the data or reload them from the db.
I also tried the <p:graphicImage> from PrimeFaces 2.X but it is not compatible with viewscope beans. Any suggestion?
That's not possible, no. The view scope is tied to a specific JSF view, which is no means of in a plain HTTP servlet request. Note that you can't access concrete request scoped beans during a plain HTTP servlet request either, they would always return null.
The session scope is the best what you can get. You can just remove the attribute from the session scope once you're finished with it in the servlet.
session.removeAttribute("somename");
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.
I was thinking to use an EJB 3 stateful session bean for this, but my research leads me to believe that a SFSB is not tied to a client's http session, so I would have to manually keep track of it via an httpSession, some side questions here . . .
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.
2) 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?
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.
I can set a JSF session scoped bean as a managed property of all of my request beans which means it's injected into them, but unlike a SFSB the JSF managed session scoped bean is tied to the http session and so the same instance is always injected as long as the http session hasn't been invalidated.
So I have multiple tiers
1st tier) JSF managed request scoped beans that deal with presentation, 1 per page.
2nd tier) A JSF managed session scoped bean that has values set in it by the request beans.
3rd tier) A stateless session EJB who executes logic on the data in the JSF session scoped bean.
Why is this so bad?
Alternative option is to use a SFSB but then I have to inject it in my initial request bean and then store it in the http session and grab it back in each subsequent request bean - just seems messy.
Or I could just store everything in the session but this isn't ideal since it involves the use of literal keys and casting . etc .. etc which is error prone. . . and messy!
Any thoughts appreciated I feel like I'm fighting this technology rather than working with it.
Thanks
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.
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.
Correction: an EJB session has nothing to do with a HTTP session. In EJB, roughly said, the client is the servlet container and the server is the EJB container (both running in a web/application server). In HTTP, the client is the webbrowser and the server is the web/application server.
Does it make more sense now?
2) 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?
Use EJB for transactional business tasks. Use a session scoped managed bean to store HTTP session specific data. Neither of both are POJO's by the way. Just Javabeans.
Why shouldn't I use a JSF SessionScoped bean for logic?
If you aren't taking benefit of transactional business tasks and the abstraction EJB provides around it, then just doing it in a simple JSF managed bean is indeed not a bad alternative. That's also the normal approach in basic JSF applications. The actions are however usually to be taken place in a request scoped managed bean wherein the session scoped one is been injected as a #ManagedProperty.
But since you're already using EJB, I'd question if there wasn't a specific reason for using EJB. If that's the business requirement from upper hand, then I'd just stick to it. At least, your session-confusion should now be cleared up.
Just in case you're not aware of this, and as a small contribution to the answers you have, you could indeed anotate a SFSB with #SessionScoped, and CDI will handle the life cycle of the EJB... This would tie an EJB to the Http Session that CDI manages. Just letting you know, because in your question you say:
but my research leads me to believe that a SFSB is not tied to a client's http session, so I would have to manually keep track of it via an httpSession, some side questions here . . .
Also, you could do what you suggest, but it depends on your requirements, until CDI beans get declarative transaction support or extended persistence contexts etc, you'll find yourself writing a lot of boilerplate code that would make your bean less clean. Of course you can also use frameworks like Seam (now moving to DeltaSpike) to enhance certain capabilities of your beans through their extensions.
So I'd say yes, at first glance you may feel it's not necessary to use a stateful EJB, but certain use cases may be better solve through them. If a user adds a product to his cart, and another user adds this same product later, but there is only one unit in stock, who gets it? the one who does the checkout faster? or the one who added it first? What if you want to access your entity manager to persist a kart in case the user decides to randomly close his browser or what if you have transactions that spawn multiple pages and you want every step to be synchronized to the db? (To keep a transaction open for so long is not advisable but maybe there could be a scenario where this is needed?) You could use SLSB but sometimes it's better and cleaner to use a SFSB..
I've noticed that when using Ajax heavy JSF 1.2 implementations like Richfaces you're somehow forced to declare more managed beans than you'll want as Session scoped so that state can be maintained across multiple Ajax requests; there are components that will just stop working.
For instance, I developed this application lately in which I had to declare almost all my JSF Backing Beans as Session Scoped in order to have component "x" working. Is there a way out of this, do you consider it a bad practice, or is just the price to pay for having Ajax enabled component in JSF 1.2.
Thanks in advance.
Session scope beans increase memory usage.
Another available scope is View Scope - This allows to keep a state of a bean between requests, while the user is still on the same view.
If you are using JSF2, please consider using #ViewScope above the bean name:
#ViewScope
public class myBean{
..
}
If you use RichFaces and JSF1.2, consider using <a4j:keepAlive /> under <f:view> in the view. for example:
<a4j:keepAlive beanName = "#{myBean}"/>
Read more info here
Another option is to use Seam conversation. Also, I wouldn't say components stop working, they still work.. it's your logic that needs to maintain some sort of state on the server.