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From "Michael Jouravlev" <jmi...@gmail.com>
Subject Re: validation breaks my form prepopulation
Date Wed, 03 May 2006 21:08:52 GMT
On 5/3/06, Kyle W. Cartmell <KyleCartmell@firstfinance.org> wrote:
> I did some tinkering and found that even though my setup action is
> indeed associated with a form bean, and my reset method is defined and
> sets my values to null, when I return to an action from a validation
> failure or forwarded from another action, the form that I originally
> used to populate the data on that page is present and intact.
>
> 1. Is it reasonable to simply make use of this mechanic to allow this
> data to persist?

How many forms do you have: one or two? If two, do they have
properties with the same names? If I remember correctly, this should
work somewhat like this:

* You submit an HTML form to a submit action, well, actually to an
action mapping
* If actionform is defined for the mapping, it is initialized. That
means, that if it has request scope, it is created. If it has session
scope it is usually reused (this is not guaranteed, but I've yet to
encounter the situation when session-scoped form was not reused).
* reset() is called on form
* form is populated from request parameters
* if "validate" attribute of the action mapping is set to true,
validate() is called
* if validate() returns non-empty object and you have "input"
attribute set, then control is forwarded to the location defined in
the "input". (Hmm, what happens if you have validate="true" but do not
have "input" attribute?) By the way, it is possible to redirect to
"input" location instead of forwarding, but this is done globally for
all mappings in the config file.
* If you do a regular forward using "input" attribute, the
request/response sequence has not been finished yet, so all objects
that were created when you submitted the request, are still there,
including request-scoped actionform and request object itself. So, if
you forward to a regular JSP page, you can pull data from the
actionform or from request object.
* Now, the fun part. If you forward to a setup action, then Struts
will look for an actionform associated with this mapping, and will
call reset() on it, then it will try to populate it from the request
object, then it will call validate() if you have validate="true". So,
if you forward to a setup action and you have changed content of the
actionform, you should either NOT associate a form with an action.
Because otherwise your changes to actionform fields will be
overwritted from the request object. Does it make sense? ;-)

> 2. I find that I am shocked by some astounding discovery regarding
> Struts functionallity, and I have gone through all of the documentation
> on the website, can anyone direct me toward comprehensive (or as close
> as possible) documentation of Struts internals in hopes that I can stop
> posting silly questions here and not have to resort to reading source?

I think that it all clears when you understand how scoped objects are
managed, and how the request/response cycle works. The key here is
that Struts runs its portion of request/response code whenever you
call an action mapping, even if you make a server-side forward.

I wrote a small article on that topic [1]. It is not perfect and,
frankly, needs a rewrite (I introduced my own names to some of the
action/form combinations), I would do some things differently. But
some sections of it are still valuable. Take a look at "Two actions,
one form" and "Two actions, two forms" sections. Currently I prefer to
use only one actionform and two action classes (input and render) for
one web resource.

Oh yeah, and as the article says, use the same scope if you use the
same form name :-) Otherwise you'll get some funny results.

Michael.

[1] http://www.theserverside.com/articles/article.tss?l=StrutsActionMapping

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