Re: How to execute bean method before JSF page is loaded?

[Jonathan Eric Miller]

Thanks for all the replies. Much appreciated. It's good to hear from other 
developers on how they've solved problems like this. I just wanted to make 
sure that using a filter to do this wasn't too far out there. So far, I've 
got it to work using both a filter and a scriptlet in the JSP. It's less 
code to do it in the JSP, but, I think I like the filter approach a little 
better as it keeps the JSP strictly for the view. I forgot that managed 
beans are only created when they are accessed. Initially, I was thinking 
they were created when the session was created. One thing that I wanted to 
double check on is, is a managed bean just a bean that is created on demand, 
or, is there more to it than that? I'm wondering if I have a bean listed in 
web.xml as a managed bean, but, then, I also create it in a filter, if that 
would cause problems? As far as I can tell it doesn't. I guess there would 
be no point of listing it as a managed bean at that point... Also, as far as 
I can tell, the managed bean is just a normal bean stored in and can be 
accessed from the HttpSession (i.e. you don't have to use 
getValueBinding()).

Jon
----- Original Message ----- 
From: "Korhonen, Kalle" <[EMAIL PROTECTED]>
To: "MyFaces Discussion" <myfaces-user@incubator.apache.org>
Sent: Friday, March 11, 2005 5:06 PM
Subject: RE: How to execute bean method before JSF page is loaded?


-----Original Message-----
From: Jonathan Eric Miller [mailto:[EMAIL PROTECTED]
Subject: How to execute bean method before JSF page is loaded?
Does anyone know if there is a recommended way to have a bean
method executed before a JSF page is loaded? For example, I
have a page with a h:dataTable in it. What I want to do is
make it so that when a user brings up the page directly (by
entering the URL in the browser text box rather than as the
result of submitting a form), a bean method is executed which
does a query to a database. I want the bean to be populated
before the page is rendered. Currently, I'm doing this using
Don't know about the recommended way, but here's a few approaches:
If your bean is request scoped, you can either initialize it in the
constructor (which is in many cases a bad idea because the bean doesn't
have the managed properties set yet) or have a special property as the
last managed property and do the initialization in its setter. If your
bean is not request scoped, you can have another request scoped bean
that is referred on your page to initialize the other bean. You could
also use Spring to initialize the beans and forward to the result page.
There's also a x:bean (or something) that you could use on the page, but
I don't like that approach because it moves some of your business logic
to the UI layer. Lastly, you can use filters.
a servlet filter. However, one problem with this is that
Faces isn't initialized at this point. This isn't a big
issue, but, one issue that I ran into is that I was using a
managed bean and that bean might not have been created by
Faces when the filter executes. So, I put some code in to
test if the bean is null or not and it creates it if
necessary. I'm wondering if there is a more recommended way
to do this within the context of Faces itself. i.e. maybe
You can initialize the Faces Context in a filter yourself if you like,
check for example
http://www.thoughtsabout.net/blog/archives/000033.html.
using a listener or something? Note, I only want the code to
execute for a specific page. It seems like there should be
some kind of onInit() method that could be overriden to
perform initialization before a page is renderered... I don't
know much about ASP.NET, but, I think it allows you to do
something like this. I guess I could use a scriptlet in the
JSP to do it.
There's a phase listener that you could for this, and it would fire on
any page, but you could program the logic yourself to do something real
only on certain views.
Kalle