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From Ted Husted <hus...@apache.org>
Subject Re: Dynamic forwardings...
Date Mon, 27 Aug 2001 11:47:01 GMT
If you are forwarding the request, then everything in the request,
including the original parameters are forwarded too. So you don't really
need to specify the parameters again. 

If you need to change the parameters, then you could generate a new
query string for the next forward, or put the value into the request
some other way. If I was forwarding from one Action to another, I might
use my own object for the parameters I was passing, and have the Action
check for that before using what was in the request. 

One likely object would be the ActionForm for the next mapping. If the
ActionForms had the tableID and itemID properties, you could pass the
information there instead of the going to the request parameters
directly.

A query string, like ?tableID=this&itemID, is what a HTML form using
type="GET" generates when it is submitted. When the controller receives
the request, it doesn't care (or really know) if the request came from
an embedded query string or a HTML form, everything is handled the same
way. 

So, an ActionForm is place to store the parameters of a GET or POST
request. If the name of the parameter matches the name of a property,
then the controller copies the value over. So form.getThis() and
request.getParameter("this") become equivalent.

If there is already an ActionForm in the request, then the controller
calls reset() and repopulates it (via BeanUtils.populate). To use an
ActionForm to pass information from one Action to another, it would
needs a "readonly" flag that would keep reset() and the other mutators
from changing any of the existing values. Since the controller reuses
ActionForms, they can be a great way pass information along -- so long
as you can keep the controller from messing with it along the way.

I can understand why people might want to generate an ActionForward with
a new set of parameters, and wouldn't vote against it, but personally it
seems like a kludge to me. Once the request is received, I believe the
expected parameters should be encapsulated in the ActionForm (thereby
documenting them), and any cross-Action communications should take place
via ActionForms. If an ActionForm is meant to be forwarded, like a value
object, then it can be written so that the mutators (including reset())
can be switched off and on.

Though, of course, whatever design works best for you is always the best
design ;-)

-- Ted Husted, Husted dot Com, Fairport NY USA.
-- Custom Software ~ Technical Services.
-- Tel +1 716 737-3463
-- http://www.husted.com/about/struts/


David Corbin wrote:
> 
> I understand the first choice presented below.  But I don't understand the
> second choice.  I think I fail to fully understand ActionForm.  Are you
> saying that if I have a populated ActionForm, then all of those arguments
> get "passed on" when I forward to another action?
> 
> ----- Original Message -----
> From: "Ted Husted" <husted@apache.org>
> To: <struts-user@jakarta.apache.org>
> Sent: Sunday, August 26, 2001 9:11 PM
> Subject: Re: Dynamic forwardings...
> 
> > You can construct ActionForwards from scratch, and I have seen people
> > include query strings with that.
> >
> > http://www.mail-archive.com/struts-user@jakarta.apache.org/msg14224.html
> >
> > Personally, I would think about adding these parameters as hidden fields
> > to the ActionForm, use the form instead, and forget about the
> > parameters. Struts automatically populates the ActionForm from the
> > parameters.
> >
> > It would also populate the same or different ActionForm for the second
> > ActionMapping if you forwarded the request.
> >
> > David Corbin wrote:
> > >
> > > I'm not sure where I'm miscommunication, so I'll go back to the
> beginning.
> > >
> > > I have an action "list".  It expects an parameter "tableID", so a link
> to it
> > > looks like "http://host/app/list.do?tableID=foo", and if things are
> > > successful, returns a page with a list of items that depend on the
> tableID.
> > > For each item, there is a link generated for action "blue" that
> specifies
> > > two parameters: tableID & itemID
> > > (http://host/app/blue.do?tableID=foo&itemID=xyzzy).
> > >
> > > No problem.
> > >
> > > The action "blue" requires the two parameters "tableID" and "itemID".
> Under
> > > certain circumstances, the results of the action blue require that
> > > "list.do?tableID=foo" be "forwarded".  Struts doesn't seem to provide a
> way
> > > to handle this last case.  If it does, I don't understand it.
> > >
> > > David
> > > ----- Original Message -----
> > > From: "Ted Husted" <husted@apache.org>
> > > To: <struts-user@jakarta.apache.org>
> > > Sent: Sunday, August 26, 2001 7:14 PM
> > > Subject: Re: Dynamic forwardings...
> > >
> > > > Typically, there would be a finite number of inputs, and you could
> have
> > > > a logical forward for each one.
> > > >
> > > > The ActionMappings form an API for the legal entry points to the
> > > > application.
> > > >
> > > > Usually, the only thing that is truly dynamic is a reference into a
> data
> > > > source, to look something up. In that case, the link tag can take one
> or
> > > > more dynamic parameters, based on the collection of beans used to
> write
> > > > it.
> > > >
> > > > In that case, the action usually gets the parameters from the request,
> > > > and uses them to look up whatever is required.
> > > >
> > > > David Corbin wrote:
> > > > >
> > > > > I'm definately talking about "forward", but my "whatever" value is
> > > dynamic.
> > > > > It's based on input (a parameter) into the action.  I don't yet
> > > understand
> > > > > the best solution for that.
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "Ted Husted" <husted@apache.org>
> > > > > To: <struts-user@jakarta.apache.org>
> > > > > Sent: Sunday, August 26, 2001 2:56 PM
> > > > > Subject: Re: Dynamic forwardings...
> > > > >
> > > > > > For a forward, you just put in an encoded query string for the
> path:
> > > > > >
> > > > > >      <forward name="itemAdd"
> > > > > >           path="/do/item/Add?code=whatever"/>
> > > > > >
> > > > > > For an action mapping, you can use the parameter property
> > > > > >
> > > > > >             <action
> > > > > >                 path="/do/item/Add"
> > > > > > ...
> > > > > >                 parameter="add">
> > > > > >             </action>
> > > > > >
> > > > > > and have the action check for the code there
> > > > > >
> > > > > > String code = mapping.getParameter();
> > > > > >
> > > > > >
> > > > > > David Corbin wrote:
> > > > > > >
> > > > > > > I've got a an action "add", which requires a an argument
"code".
> > > > > > > One (at least) of the possible forwards needs to specify
this
> "code"
> > > on
> > > > > the
> > > > > > > forward URL.
> > > > > > >
> > > > > > > How can I do that?
> > > > > > >
> > > > > > > Thanks
> > > > > > > David Corbin
> >
> >

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