ActionMapping.getAttribute()

[Howard Miller <me...@howardmiller.co.uk>]

Hi,

Confused again....

short question.... what does the method ActionMapping.getAttribute() do?? The 
javadoc for it is a bit terse!

Longer version... I'm working through the struts-example (carefully) this time, and it 
keeps turning up - I simply can't see what its for. In particular in 
EditRegistrationAction.java it is used to store the RegistrationForm bean that is 
created. Why is that done? I would have thought that is a bean is stored in the 
request or session scope it would just have a constant value - not this mystery value - 
what am I missing?

While on the subject, (and I suspect related) - what does ActionMapping.getScope() 
do? I don't get how an Action can have a scope and/or an Attribute. What's the 
story??

Howard Miller

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Re: ActionMapping.getAttribute()

[Eddie Bush <ek...@swbell.net>]

You specify with an action declaration which scope you want your form 
bean to be placed in.  There is a contract between actions/form beans 
that guarantees the form bean to be instantiated before the action is 
called (assuming you specified the form to be used in your config).  So, 
you see, scope is highly relevant (we could elect to put all forms in 
request scope, rather than session [ which is the default]).  Now, 
coupled with this, we have the idea that the user may want to specify 
their own key under which the form may be found.  I'm not sure exactly 
why that's there, but let me take a stab at it (guys, feel free to 
correct me!).

Under most circumstances, you don't need to specify a value for 
"attribute" because Struts is going to use a given key automatically (I 
can't think of what it is right now) to place your bean into <whichever> 
scope and retrieve it from that same scope - it's got to have a name and 
it has to know under which scope that name is valid :-)  Ok, so why not 
just use the default all the time?  Well, what if you had a bean you 
wanted to be used as a form bean?  OR - what if you wanted to do 
something with a session-stored form ... say you wanted to reference an 
attribute of it.  Ok, because you have this nifty "attribute" property, 
you're able to give a succint name to the form.  You can now have Struts 
use some custom bean to act like a form (better derive it from 
ActionForm though!) or reference a session-scoped form in subsequent 
pages to ... output a field, for example.  Say it were a user 
registration form and it contained their name.  You could reference the 
form to display their name.

While I'm sure I'm not far off, I'm equally sure someone else can give 
better treatment to this :-)  Hopefully that helps some.  In any case, 
it sounds like you're rather new to Struts - I wouldn't bother trying 
any advanced features (of which I would say this is one) right off. 
 Rather, sit down and build up a "teach myself Struts" app and build on 
it incrementally - adding (useful) "advanced features" as you go.  While 
sitting down and learning all of the classes would certainly be a good 
exercise too, I think you would gain more (IMHO) from actually building 
something.

Howard Miller wrote:

>Thanks Eddie,
>
>That's interesting, *but* what does the attribute of an ActionMapping actually *mean*, 
>why would I want to use it?
>
>I think I've completely failed to understand some important concept! I don't see how a 
>mapping has a concept of scope when it belongs to an Action, not a FormBean or 
>similar.
>
>Howard Miller
>

-- 
Eddie Bush




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Re: ActionMapping.getAttribute()

[Howard Miller <me...@howardmiller.co.uk>]

Thanks Eddie,

That's interesting, *but* what does the attribute of an ActionMapping actually *mean*, 
why would I want to use it?

I think I've completely failed to understand some important concept! I don't see how a 
mapping has a concept of scope when it belongs to an Action, not a FormBean or 
similar.

Howard Miller

On 1 Oct 2002 at 16:54, Eddie Bush wrote:

> attribute is an ... attribute (bit confusing) of an ActionMapping.  The 
> getAttribute() method returns the value of the attribute attribute - or 
> the name attribute if the attribute attribute is null.  ActionMapping 
> actually inherits this from ActonConfig (in o.a.s.config) so the proper 
> javadoc for it (if it exist) would be found there.
> 
>     /**
>      * The request-scope or session-scope attribute name under which our
>      * form bean is accessed, if it is different from the form bean's
>      * specified <code>name</code>.
>      */
> 
> That's the javadoc comment for the attribute attribute - taken from 
> ActionConfig.java.  So the attribute attribute, then, specifies the name 
> under which we can find the form-bean associated with this action - 
> whether it is stored in request or session scope is specified by a 
> different attribute - scope.
> 
> Questions on this level can most easily be answered by consulting the 
> source :-)  Go checkout a copy from CVS (if you can) or grab a copy of 
> the latest source release (beta 2 - some of it has been updated, but for 
> questions such as this it's still valid I believe).  I wish they'd do 
> nightly source snapshots too ...
> 
> Howard Miller wrote:
> 
> >Hi,
> >
> >Confused again....
> >
> >short question.... what does the method ActionMapping.getAttribute() do?? The 
> >javadoc for it is a bit terse!
> >
> >Longer version... I'm working through the struts-example (carefully) this time, and it 
> >keeps turning up - I simply can't see what its for. In particular in 
> >EditRegistrationAction.java it is used to store the RegistrationForm bean that is 
> >created. Why is that done? I would have thought that is a bean is stored in the 
> >request or session scope it would just have a constant value - not this mystery value - 
> >what am I missing?
> >
> >While on the subject, (and I suspect related) - what does ActionMapping.getScope() 
> >do? I don't get how an Action can have a scope and/or an Attribute. What's the 
> >story??
> >
> >Howard Miller
> >
> 
> -- 
> Eddie Bush
> 
> 
> 
> 
> --
> To unsubscribe, e-mail:   <ma...@jakarta.apache.org>
> For additional commands, e-mail: <ma...@jakarta.apache.org>
> 
> 



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Re: ActionMapping.getAttribute()

[Eddie Bush <ek...@swbell.net>]

attribute is an ... attribute (bit confusing) of an ActionMapping.  The 
getAttribute() method returns the value of the attribute attribute - or 
the name attribute if the attribute attribute is null.  ActionMapping 
actually inherits this from ActonConfig (in o.a.s.config) so the proper 
javadoc for it (if it exist) would be found there.

    /**
     * The request-scope or session-scope attribute name under which our
     * form bean is accessed, if it is different from the form bean's
     * specified <code>name</code>.
     */

That's the javadoc comment for the attribute attribute - taken from 
ActionConfig.java.  So the attribute attribute, then, specifies the name 
under which we can find the form-bean associated with this action - 
whether it is stored in request or session scope is specified by a 
different attribute - scope.

Questions on this level can most easily be answered by consulting the 
source :-)  Go checkout a copy from CVS (if you can) or grab a copy of 
the latest source release (beta 2 - some of it has been updated, but for 
questions such as this it's still valid I believe).  I wish they'd do 
nightly source snapshots too ...

Howard Miller wrote:

>Hi,
>
>Confused again....
>
>short question.... what does the method ActionMapping.getAttribute() do?? The 
>javadoc for it is a bit terse!
>
>Longer version... I'm working through the struts-example (carefully) this time, and it 
>keeps turning up - I simply can't see what its for. In particular in 
>EditRegistrationAction.java it is used to store the RegistrationForm bean that is 
>created. Why is that done? I would have thought that is a bean is stored in the 
>request or session scope it would just have a constant value - not this mystery value - 
>what am I missing?
>
>While on the subject, (and I suspect related) - what does ActionMapping.getScope() 
>do? I don't get how an Action can have a scope and/or an Attribute. What's the 
>story??
>
>Howard Miller
>

-- 
Eddie Bush




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