Hello everybody,
First, I want to apologise for the fact that my previous message was
posted multiple times in this mailing list. Our sendmail log sent it
only once, so I do't really understand what went wrong.
Back to the issue. Consider the following case we're dealing with in our
application:
We're working on an e-commerce application with which people can order
different kind of products. Ordering a product consists of two parts:
first they have to fill in a product specific form to get a price quote
for the requested product. Then, if they accept the quote, they have to
fill in address information for delivery. Filling in address information
uses the same form for all different products.
What we want to do is the following:
For each product, we define an action in struts-config.xml. Each action
uses an own, product specific form, say productAFrom, productBForm
etcetera. Each of these forms is an extension of an abstract class
productForm.
For the address information part, we want to define one additional
action in struts-config.xml, which uses the abstract productForm as
form-bean.
Since filling in the address information form always follows the product
ordering form, we know that the user always has a productForm stored as
attribute in his session.
I do realize that this mechanism gives some more responsibility to the
developer, in that he has to be careful using an abstract class name as
the type of a form bean, but I don't know any better alternatives yet.
Maybe using the same conventions as jsp:usebean, create a new instance
of an action form only if a 'class' attribute is present, if just a
'type' attribute is present only try to recycle existing instances.
Any suggestions?
Ronald Bakker
Virgil PM&C
"Craig R. McClanahan" wrote:
>
> On Mon, 6 Aug 2001, Ronald Bakker wrote:
>
> > Hi everybody,
> >
> > In Struts, form-beans can be described by 'name' and 'type'. Looking at
> > method 'processActionForm' in ActionServlet, I conclude that roughly the
> > following is happening (correct me if I'm wrong):
> >
> > When trying to find a form-bean from a mapping, Struts tries to find an
> > attribute with the given 'name' in the scope that is defined for this
> > mapping, if the class name of the found attribute is equal to 'type' it
> > will reuse this found attribute. Otherwise a new form-bean instance of
> > class 'type' is created and placed in scope.
> >
>
> That's a correct understanding.
>
> > To my opinion, one fallback of this implementation is that you are
> > forced to use the implementing class name of the form-bean you intend to
> > use, you are not able to use an interface or abstract class name. Is
> > there any chance Struts is going to use a more flexible way of
> > retrieving form-beans from a mapping? I would like Struts to use the
> > same mechanism as jsp:useBean, where you are more flexible in using
> > beans with either 'type' or 'class'.
> >
>
> Remember that <jsp:useBean> has a restriction -- if the bean is not
> already there in the correct scope, you *must* have specified the actual
> class name so that <jsp:useBean> can instantiate it. Struts will often
> (and, if you're using request scope form beans, *always*) need this
> information anyway, for the same reason.
>
> > Right now, we replaced this part of processActionForm with an own
> > mechanism of reusing form-beans:
> >
> > /**
> > * Original Struts code:
> > */
> >
> > // Can we recycle the existing form bean instance?
> > if ((instance != null) &&
> > className.equals(instance.getClass().getName())) {
> > if (debug >= 1) {
> > log(" Recycling existing ActionForm bean instance of class '"
> > + className + "'");
> > }
> >
> > return (instance);
> > }
> >
> > /**
> > * Replaced by our code:
> > */
> >
> > // Can we recycle the existing form bean instance?
> > try {
> >
> > if ((instance != null) &&
> > Class.forName(className).isInstance(instance)) {
> > if (debug >= 1) {
> > log(" Recycling existing ActionForm bean instance of class '"
> > + className + "'");
> > }
> > return (instance);
> > }
> > }
> > catch (ClassNotFoundException ce) {
> >
> > if (debug >= 1) {
> > log(" Class not found: '" + className + "'");
> > }
> > return null;
> > }
> >
>
> I can see what you're after, but won't this only work in the case of
> session beans that were previously created by an Action? For anyone else,
> you'll just get an instantiation error.
>
> Note to self -- if we change the logic here, a similar change will be
> needed inside the <html:form> tag, which can also create the form bean
> dynamically if needed.
>
> > Ronald Bakker
> > Virgil PM&C
> >
>
> Craig
