Monday, 13 May 2013

JSF 2.2 Stateless views explained


The JSF 2.2 specification (JSR-344) is recently approved. There are a few examples available but there seems no detailed explanation yet of the new features.
Although the development is still in progress, I like to start today already with the stateless view features which was fairly late added to the list of JSF 2.2 features.
The ticket had many votes and stateless is hot, so for many people this is a very wanted feature which is added.
But be aware of the implementation details and some other facts that are very good explained in this section of the excellent overview of Arjan Tijms on JSF 2.2 features.


The explanation of the feature is fairly simply. By specifying the attribute transient on the f:view tag, we are able to run that page in a stateless mode. Stateless here means that the JSF StateManager isn’t storing any data into the memory related to this view.
During restore view phase, the view is created, as always, but now there isn’t any state applied to it.
It is a fairly simple change but has a lot of consequences.

viewScoped beans

The most important effect of the stateless operation mode is that all viewScoped beans are lost. Those kind of beans, tied to a certain view, aren’t stored anymore and thus, when the same page is rendered again, a new version of the bean needs to be instantiated again.
It can easily demonstrated by a ‘classic’ scope testing application, for example the one I used here to test CODI on WLS 12c server. You create beans with a different scope, like requestScope, viewScope, sessionScope and applicationScope and initialize a timestamp in the constructor.  The value of this property is then shown on screen where you can do a post to stay on the same page or go to another page which has the same beans on it.
In the case of the transient view, even if you stay on the same page, a new instance of the viewScoped bean is created. The other scopes aren’t affected.
I tried this with the Glassfish 4 promoted build 87 and a Tomcat 7 instance where I used the latest available Mojarra 2.2 snapshot.

viewScope != viewScope

Although not immediately linked to the stateless view features, there are now 2 ViewScoped annotation classes. We had already the RequestScoped, SessionScoped and ApplicationScoped from JSF (package javax.faces.bean) and the CDI version (in package javax.enterprise.context).
As requested by many developers, there is now also a CDI version of the ViewScoped (from package javax.faces.bean) but defined in JSF (and not CDI). The new class is defined in javax.faces.view. Look careful to import the correct class in relation to the @ManagedBean or @Named annotation because mixing them will lead to unexpected behaviour.

When to use

What are the use cases for the stateless view operation mode. As already mentioned in the feature description by Arjan Tijms, performance and memory gain is minimal, except when you are working with very large pages that contains thousands of components.
Besides the fact that ViewScoped beans behave differently, a lot of components are relying on the fact that they can save and restore their state within the view. So many components, standard ones but also from component libraries like PrimeFaces will not function properly anymore on stateless views.
On the other side, views are stateless and this means you can even post your data back to the server, after your session has expired or even after a server reboot.


Since there is a large impact on AJAX behaviour, commonly used with ViewScoped beans, and the proper functioning of components, considering stateless views must be evaluated thoroughly and tested very profound.
And initiatives like the one from Industrie IT should also be considered when you are interested in those kind of setups.