Improve page session attributes resolution

[avpinchuk]

This PR based on very detailed @OndroMih's comment.

What happens:

• If pageSession explicitly requested, return it
• Else if pageSession not found or doesn't contains property, return null
• Else if property present in pageSession, check standard scopes (request, view, session and application) for an updated value
• Else return value from our custom page session.

This generally emulates behavior as for Jakarta Server Faces 3.0 VariableResolver Chain Wrapper.

I reverted from store page session to view map, because view map cleared on an every call of the FacesContext.setViewRoot() and we cannot control each call of this method.

[avpinchuk]

@arjantijms, @hs536, @OndroMih what you thinks?

[OndroMih]

How does this work? How does this set a page context value? Before, this method expected base == null and property != null and set the property into the page context. This means I think that if a page set some variable (with no base), the variable was added to the page context.

The method after your change expects that base != null, which is different to the condition before. And it doesn't set anything in the page context. What happens if a page just defines a new variable (without base) ?

[avpinchuk]

Prior to Faces 4, PageSessionResolver was VariableResolver, not ELResolver and therefore did not setup any values.

All page session values are set with our custom handlers, e.g. setPageSessionAttribute.

Now we first try to read updated values, which come to us from standard scopes, and if its not found, read from page session map.

[OndroMih]

OK, I understand, thanks :)

[avpinchuk]

@OndroMih, page session attributes are "read-only" from the point of view EL engine, imo. Here description from spec https://jakarta.ee/specifications/faces/3.0/jakarta-faces-3.0#a2773.

I tried to implement this part in the getValue() method

Get the head of the VariableResolver chain and call resolveVariable(facesContext, property) and return the result

by checking standard scopes before our custom page session scope. This should prevent us from reading an obsoleted values.

Updates of the values from requests handled by Faces ScopedAttributeELResolver.

[OndroMih]

Looks good to me.