Hi Andrew,
Let's imagine we have declared a backing bean as request scoped (say cat).
On submit of a form that contains information related to that bean, even
though we have specified in the form value attributes that we point to a
bean with the given name (eg: value="#cat.color"), there isn't any attempt
to verify if a backing bean with that name was declared (naturally if it
isn't already in any scope).
I'm new to JSF and I tried an example like this, thinking the framework will
recognise I'm trying to fill request parameters prefixed with "cat" into my
declared request scope bean with the same name, but when I aquired
control "at the application scope" I didn't find any bean under the key
"cat" in my request.
*explanations : I'm not very good in english, maybe I was misunderstood:*
- There is nothing in the HttpServletRequest JavaDoc that says you
cannot set request attributes at any time once the request has been
created:
- I said that before the MVC frameworks, when we had only servlets
and jsps, it wasn't possible to intercept the request and add it
attributes,
all we had was what comes from the HTTP protocol: *parameters*.
Now that we now what data model is expected on the other side, we can
understand that when a parameter has a given naming pattern, it
is designed
to fill the corresponding model data.
- Instantiating beans before
they have been referenced would create performance and logic bugs in
JSF applications.
- Instantiating all the declared request beans will lead to even
worser results than the actual, because for every request
lifecycle we will
have all the possible beans in memory, plus the overcomputation of the
instantiation. What I meant was: by the name "pattern" of UIComponent's
value attribute, we can understand that a UIComp is supposed to fill the
field of a - page, request, session or application scoped - bean with the
name "cat" (again :-)). If we happen to have in our faces-config
a bean with
the name "cat", and that theresn't any bean instanciated in the server
memory (in any scope) with this same name, so we are the most probably
trying to instanciate the declared bean and profit from all JSF phases to
have a validated and ready to use bean. If it happens that the value
attribute didn't mean *that* bean (I mean not the one declared
in the faces-config) than the user would rather rename his bean because
sooner or later, he will get bad surprises. (All the constraints it adds
is a sort of type checking, and no one will say that adding type
checking is
bad for safe programming)
I agree there are conditions to instantiate the bean without adding bugs
(like putting a bean in the request, so hiding the original one that was in
(or will be added to) the session), but cases like this are very probably
developper errors because using the same name in two scopes is definitly a
bad practice. Cases like this could be discouraged by warning logs.
Otherwise, I don't see where there can be logic bugs, but the question needs
certainly more reflection.
2007/6/20, Andrew Robinson <[EMAIL PROTECTED]>:
Beans are created on an as needed basis. Instantiating beans before
they have been referenced would create performance and logic bugs in
JSF applications.
If you want to force the instantiation of beans at a given time,
simply ask them to be created in a phase listener.
The following code will force that an instance is created:
application.createValueBinding("#{beanName}").getValue(facesContext);
BTW, why can't you set a request attribute in a phase listener in the
before restore view phase?
There is nothing in the HttpServletRequest JavaDoc that says you
cannot set request attributes at any time once the request has been
created:
http://tinyurl.com/29ypjz
Even though I proposed a means to force the creating of request beans,
I don't see a valid use case for this. What are you trying to do that
would need to force a request bean to be created before a view is
restored? If you can answer that perhaps we can help find another way
of doing what you want with better design and performance metrics.
-Andrew
On 6/20/07, Zied Hamdi <[EMAIL PROTECTED]> wrote:
> Hi MyFaces people,
>
> I'd like to ask a question that leeded me to an interesting concusion:
>
> Why now that we are in a "managed" environement can't we still use the
> request attributes for incoming requests (to the server)?
>
> It's not complicted to have backward compatibility with the servlet
> specification, request attributes can't exist when we enter the
> Servlet.service() method. So now that we know that, we know that we
can't
> override an existing attribute if we create one in the restore view
phase of
> JSF. So why don't we create request scoped backing beans in this phase
so
> that we avoid unnecessary session obesity.
>
> The idea is that with the current design of JSF, we must have for every
data
> object (let's say data objects instead of DTO for objects that go to the
> front end) an instance living in the session scope, and everybody knows
that
> we don't matter if they are not reset to null when we don't need them.
The
> use case is that we usually need one of them at a time. But putting them
in
> the request scope isn't sufficient because they are not transferred to
the
> next request where we need to get the user entred values. If they were
> created in the restore view phase, they would live longer and we could
> profit of their existence for all the cycle instead of having them at
the
> moment the page is being displayed.
>
> I thing the way it's done today is historical: nothing was managed
before
> JSF and Struts, and we pay today for that historical technical
constraint
> (that it isn't possible to pass attributes in the HTTP protocol). To
compare
> the problem: with Struts, the memory can be released from the server as
soon
> as the action has finished its execution...
>
> --
> Zied Hamdi
> zatreex.sourceforge.net
--
Zied Hamdi
zatreex.sourceforge.net
