Keep bean attributes after ajax form submit - ajax

Question

I have a #ViewScoped #ManagedBean which creates an unique ID. This ID is rendered in a form like:
<h:form>
<h:outputText value="#{myBean.uid}" id="uid"/>
<h:hiddenInput value="#{myBean.uid}" id="hiddenId" />
....
<p:commandButton actionListener="#{myBean.create}" ajax="true" update="#form" value="Create" />
</h:form>
So far so good. On first request the page is rendered correctly. After submitting the form and in the case of validation failure, the outputText is empty but the hidden input field keeps its variable.
Any clue what I'd have to do to prevent this behavior and too let the outputText keep its state?
I realized that the bean seems to be initialized after each ajax request. But then, why does the hidden input field keeps the old variable?
Here is the relevant code of my bean:
#ManagedBean(name = "myBean", eager = true)
#Stateful
#Model
#ViewScoped
public class MyBean implements Serializable {
...
private String uid;
...
#PostConstruct
public void initWithData() {
this.uid = UUID.randomUUID().toString();
}
}

Answer 1

JSF input components have 3 places where the value (the state) is stored:
Submitted value (the raw unconverted/unvalidated String request parameter value).
Local value (the successfully converted/validated object value, stored inside component itself).
Model value (when the entire form is successfully processed, stored as bean property)
JSF processes input components as follows:
Get HTTP request parameter value by component's client ID and store it as submitted value.
If conversion/validation succeeds, set it as local value and set submitted value to null.
If entire form is successfully processed, set it as model value and set local value to null.
JSF renders values of input components as follows:
If submitted value is not null, display it.
Else if local value is not null, display it.
Else display model value.
So, in your particular case of a general validation failure, JSF is for that hidden input component just redisplaying the local value instead of the model value. If you want to achieve the same with the output text, I think best is to just do the same as JSF:
<h:outputText value="#{empty hiddenId.submittedValue ? empty hiddenId.localValue ? hiddenId.value : hiddenId.localValue : hiddenId.submittedValue}" />
<h:inputHidden id="hiddenId" binding="#{hiddenId}" value="#{myBean.uid}" />
Alternatively, you could just use a read only input and remove the border by CSS if necessary:
<h:inputText id="hiddenId" value="#{myBean.uid}" readonly="true" style="border: none;" />
As to your bean, I'm not sure what's happening there as this class seems to be extremely tight coupled. I'd rather split it into 3 classes: one real backing bean, one stateless service and one model entity. Further, you should also make sure that you aren't binding view build time tags or attributes to a property of a view scoped bean. Otherwise it will indeed guaranteed be reconstructed on every single request.
See also:
JSTL in JSF2 Facelets... makes sense?
#PostConstruct method is called even if the ManagedBean has already been instantiated (e.g. on AJAX-calls)
By the way, the eager=true has only effect in #ApplicationScoped beans.

Answer 2

The problem is probably the #Model stereotype (was, as you already removed it). It combines #Named and #RequestScoped and makes the bean a CDI request scoped bean. CDI managed beans should be resolved before JSF managed beans and therefore the #ViewScoped has no effect (it creates a JSF managed bean).