The issue, IMO, lies with <tc:in/> and not #{cat}. The value,
#{cat.color} is being evaluated by the component in the render
response phase, and thus when the variable resolver sees a base of
cat, it finds it as a managed bean, and sees that it hasn't been
instantiated yet, and thus creates it.
If <tc:in/> is bound to a component that extends UIInput or implements
EditableValueHolder, then it is the job of that component to decode
the value during the processing of decoding. Typically what happens
with UIInput:
processDecodes calls decode
decode calls the decode of the Renderer for the component
the Renderer looks in the request parameters for whatever data it expects
if data is found, it sets the submitted value on the component
processValidators is called which in tern, calls validate. If there is
no submitted value (null), nothing happens. If there is a submitted
value, validateValue is called. validateValue converts the submitted
value to a local value using the converter (if any). (so
getLocalValue() now returns a value). If any validation fails,
renderReponse is called on the faces context and we skip to the render
phase
processUpdates is called. This now calls updateModel. This now gets
the ValueBinding for the "value" attribute/property and calls set on
it. This is where #{cat.color} will be resolved and set to the new
value.
As you can see, unless your component has any reason at all to use its
value attribute before updateModel, then it will never be called (and
thus your cat will not meow, er sorry, will not be created).
If you are only seeing cats in the rendering then you are not getting
to the updateModel phase (or your <tc:in /> isn't a UIInput
component).
So by your example, I don't see how this relates to backing bean
instantiation but rather what <tc:in/> is and what the job of that
component is.
BTW, if you are not seeing the value getting updated, check for messages.
As for request attributes, I am still not seeing what you are using
them for (are you using them to pass data between servlets, jsp pages
and jsf views?).
If for some business reason you need to force the instantiation of a
component early, you could write a custom component and put it in the
page that when restoreState is called (during the restore view), it
calls:
ValueBinding vb = getValueBinding("value");
if (vb != null) vb.getValue(getFacesContext());
That will force the "value" attribute to be evaluated, and if that is
your #{cat.color}, the cat bean will be created.
-Andrew
On 6/21/07, Zied Hamdi <[EMAIL PROTECTED]> wrote:
> Hi Andrew :-),
>
> The question wasn't well asked, I'm sorry. I will try my best:
>
> Today if JSF receives a request from a form that has in its component list
> the element ( <tc:in value="#{cat.color}"> ) and that none of the scopes has
> the attribute "cat" stored in it, the request parameter will rest as is: no
> action will be exerced in the UPDATE_MODEL_VALUES phase.
>
> And this will happen even if we have declared a backing bean with the name
> "cat" (in any of the scopes). The backing bean "cat" will be created at the
> RENDER_RESPONSE phase because it's there! that it will realize through its
> VariableResolverImpl that it needs a backing bean with that name and that
> it's still not instantiated.
>
> Now if the backing bean "cat" is session scoped, the first RENDER_RESPONSE
> will instantiate the bean, so it's not possible to have an incoming form
> request without having an already instantiated backing bean (as long as the
> request is coming from the same application).
>
> The problem is when the backing bean "cat" is request scoped: the first
> RENDER_RESPONSE will instantiate the bean and add it to the request
> attributes, but when the request life cycle is finished (the page is
> displayed), the attribute will die with its request. So when we submit the
> form, we are again in a blank situation (no bean in any scope), until we
> arrive to the RENDER_RESPONSE phase. Again there it's too late, the
> INVOKE_APPLICATION phase has passed and no added value was done by the JSF
> framework.
>
> The idea is to detect the need for a backing bean before the
> INVOKE_APPLICATION phase, and to have the bean populated at that phase. So
> insted of waiting until we reach the RENDER_RESPONSE phase, we can do our
> checks and instantiations in the UPDATE_MODEL_VALUES.
>
> Now let's discuss the bugs that may result from this design change:
>
> The developer may want to control the creation time of the backing bean, in
> that case, he doesn't need a backing bean but a standard request attribute.
> The developer may have its own attributes in the request and see them
> overriden by JSF (because request parameters happen to be interpreted by JSF
> as a request for backing bean instantiation): we can log a warning in this
> case and do not instantiate the backing bean. But I saw in your that you
> agree it's not a good idea to have attribute naming conflicts, so the
> warning can only be a compilation runtime extention.
> I hope you understood what I mean, I'm sorry for writing so long mails and
> taking your time, but the idea seams important to me...
>
> Regards,
> Zied Hamdi
>
>
>
> 2007/6/21, Andrew Robinson <[EMAIL PROTECTED]>:
> > It sounds like you are simply asking about the name resolution from
> > the EL engine. If that is the case, then there may be different
> > options for you, but I am not sure if I still understand your use case
> > all the way.
> >
> > If it is about name resolution, then the best place I can send you is
> > to the MyFaces source code. If you open
> >
> > org.apache.myfaces.el.VariableResolverImpl
> >
> > You will see the source that is responsible for resolving JSF variable
> > names in the MyFaces implementation.
> >
> > When someone asks for "#{cat}", it will check in order:
> >
> > 1) built-in (facesContext for example)
> > 2) request
> > 3) session
> > 4) application
> > 5) managed bean
> >
> > Therefore if you have "cat" mapped in the servlet application scope
> > and a bean named "cat", you will only get one from the servlet
> > application scope and never the managed bean. If you have two managed
> > beans with the same name, one is booted and never will be returned
> > (hence the warnings).
> >
> > Think of the managed beans as being registered in a Map. Only one
> > value is possible.
> >
> > If you are having name conflicts, I would suggest using EL naming
> > patterns. This could be XML namespace style, java package style, or
> > your own custom style.
> >
> > So instead of "cat", you could use "requestscope-cat" or
> > "request-com-mycomp-cat" or whatever.
> >
> > Now if you still want more functionality, then may I suggest looking
> > into writing your own VariableResolver by extending the one from
> > MyFaces or look into writing your own property resolvers (see
> > faces-config information or other JSF specification information for
> > information on these).
> >
> > Hope that helps some,
> > Andrew
> >
> >
> > On 6/20/07, Zied Hamdi <[EMAIL PROTECTED] > wrote:
> > > 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
> >
>
>
>
> --
>
> Zied Hamdi
> zatreex.sourceforge.net
