Challenge with dynamic rendered content

Question

I have a complex JSF file that I want to conditionally render a portion of the page based on a dynamic value. Here is the simplified scenario.
<h:form>
<h:inputHidden value="#{aRequestScopedMbean.id}"/>
<h:outputText value="JSF rocks" rendered="#{aRequestScopedMbean.showValue}"/>
</h:form>
...The JSP's mbean has an id value binding which is key to determining the return value of aRequestScopedMbean.showValue. In other words the getShowValue method uses the id to determine its return result. Unfortunately, during server side processing, it appears that during the early JSF phases (I believe the restore view phase) the framework tries to determine the result from our showValue method, but that method fails because the id has not yet been restored.
I must be missing something as this scenario seems fairly simple. The only solution that I can devise is to put the id as a session scoped variable, that is a viable solution for this trivial case, but that won't suffice because the actual pages that I'm working with would contain too much session data.
What am I missing?
Thanks,
Josh.

Answer 1

I don't think you are missing anything. That's just how it works.
The rendered component property is checked many times within the lifecycle as the lifecycle methods are applied to the component tree.
As you already seem to know, the problem is that your showValue expression is being called before you set the id value. Here are a couple suggestions:
1. You can try to "send" the id parameter to your managed bean as an HTTP parameter. You can then set the id property on your managed bean using the managed-property element. Something like:
<managed-bean>
<managed-bean-name>aRequestScopedMbean</managed-bean-name>
<managed-bean-class>foo.aRequestScopedMbean</managed-bean-class>
<managed-bean-scope>request</managed-bean-scope>
<managed-property>
<property-name>id</property-name>
<value>#{param.id}</value>
</managed-property></managed-bean>
The setId() method will be called right after the constructor is done and this will be before your showValue method is called.
2. It might be possible to ask the FacesContext what phase it's in or something similar and use this information in your showValue method (although that seems very messy and prone to error)
3. As you suggest, persist the id in session. Though, as you also point out, this has it's drawbacks as well.
In any case, you must devise a way to populate your id value before showValue gets called.