Manisha Menon wrote:
> Thank you craig.
>
> I am definitely looking at the struts framework today.
> But can you please enlighten me about the action
> dispatcher in the framework.
>
In Struts (as in many other people's MVC-type frameworks discussed on
this mailing
list over the last year or so), the controller servlet uses the request
URI to
choose what "action" needs to take place. My favorite way to do this is
mapping
the servlet to the "*.do" extension, so you might have a form submit to
a URL like
"saveCustomer.do" -- the "do" implying "go do something". Note that the
JSP page
itself has no notion of what piece of business logic is going to respond
to this
request -- it is separated from the internal organization of the
server-side code.
When the controller servlet is started, part of the configuration is a
set of
mappings from the various request URIs to "action" classes -- that is,
those that
implement the Action interface. The first time you use a particular
action class,
the controller servlet instantiates an instance of the corresponding
class (saving
this instance away for use later), and calls the perform() method of the
action
class. The perform() method initiates the appropriate actions, and then
returns an
ActionForward object identifying the JSP page (typically) which should
be used to
display the next stage of the user interface. (For those of you
following my
descriptions of "Model 2", this is a new feature that was suggested
during our
discussions.) The forwarding object is typically looked up by logical
name, so you
can say "please forward to the List Customers" page, without knowing
what the
actual JSP page name is -- again, working towards separation of the
layers in the
MVC pattern.
NOTE: Tonight's nightly build of Struts, at
<http://jakarta.apache.org/struts>,
will contain the most up-to-date version of these features.
>
> I sincerely thank you for showing some direction.
There have been numerous discussions of this general design pattern on
JSP-INTEREST
over the last year or so. Access the archives of this list
<http://archives.java.sun.com> and search for the term "Model 2" to see
some of
these discussions.
>
> Manisha.
Craig
>
> --- "Craig R. McClanahan"
> <[EMAIL PROTECTED]> wrote:
> > Manisha Menon wrote:
> >
> > > Hi Craig,
> > >
> > > Exactly ! We have done in the same way.
> > >
> > > 1. Getting the action name from the hidden field.
> > > String action_name =
> > > request.getParameter("ACTION_NAME");
> > >
> > > Then instantiating the business object in either
> > of
> > > the following ways.
> > >
> > > a) BusinessInterface businessObject =
> > (BusinessObject)
> > > action_name;
> > >
> > > b) BusinessInterface businessObject =
> > >
> >
> BusinessObjectfactory.createBusinessObject(action_name);
> > >
> > > But I would like to know from you, whether this
> > > approach is not running short of anything ?
> > >
> > > I have seen few of the approaches made use of
> > event
> > > delagation methodology. Can someone explain that
> > > methodology in web context and also a possible
> > > comparison between the two ? I am sorry if I am
> > trying
> > > to bring something unusual here.
> > >
> > > Thank you foryour replies,
> > >
> > > Manisha
> > >
> >
> > This doesn't directly address your questions, but
> > you might want to take a look at
> > the Struts framework at
> > <http://jakarta.apache.org/struts>, which provides a
> > fleshed out framework for the MVC controller servlet
> > and action dispatcher, plus
> > some nice support for dealing with forms and
> > internationalized applications through
> > a JSP custom tag library.
> >
> > For simple applications, I implement my business
> > logic in the action class that
> > gets invoked by the controller servlet. For more
> > complex needs, I think of the
> > action class as following the "adapter" design
> > pattern, translating the HTTP
> > request parameters into appropriate property setter
> > calls on business logic beans
> > (either EJBs or regular JavaBeans). The business
> > logic beans, then, are insulated
> > from the fact that they were invoked in a web
> > application, so you can reuse them
> > elsewhere.
> >
> > Craig McClanahan
> >
> >
> > >
> > > --- "Craig R. McClanahan"
> > > <[EMAIL PROTECTED]> wrote:
> > > > Manisha Menon wrote:
> > > >
> > > > > Hi all,
> > > > >
> > > > > I know the question is very silly, but I am
> > sorry
> > > > I
> > > > > could not avoid asking your help.
> > > > >
> > > > > I follow the MVC design methodology in my web
> > > > > framework which has got servlets, jsp and
> > beans.
> > > > >
> > > > > JSP page forwards the request to the
> > controller
> > > > > servlet requesting for a certain action.
> > > > > The servlet controller after receiving the
> > request
> > > > > object,instantiates the appropriate
> > > > > business bean, which will use connection pool
> > > > manager
> > > > > and data access beans for manipulating
> > > > > the data. After completing the data handling
> > > > > operations, the servlet
> > > > > controller returns the manipulated data back
> > to a
> > > > new
> > > > > JSP page.
> > > > >
> > > > > Now my question :
> > > > >
> > > > > How is the conversion/ translation of the
> > action
> > > > (say
> > > > > for example updation, insertion or deletion)
> > which
> > > > is
> > > > > coming from the client JSP page done by the
> > > > controller
> > > > > servlet taken to the
> > > > > right instance of business bean ? A single
> > page
> > > > may
> > > > > have more than one action. Now, how do the
> > > > controller
> > > > > servlet calls the UpdateBusinessBean for
> > update
> > > > action
> > > > > and InsertBusinessBean for insert action ? The
> > > > method
> > > > > that will be used by the client to invoke the
> > > > servlet
> > > > > is "POST". Can I ask you, what are the
> > possible
> > > > ways
> > > > > of doing this, (Already I have adopted one
> > method
> > > > in
> > > > > my last assignment, but I am not too happy
> > about
> > > > it,
> > > > > as it did not consider scalabilty issues and
> > also
> > > > it
> > > > > was tightly coupled.)
> > > > >
> > > > > Manisha
> > > > >
> > > >
> > > > In a "database maintenance" application like
> > what
> > > > you describe, it is common to
> > > > have a single action class that is called upon
> > to
> > > > perform slightly different
> > > > actions (such as an INSERT for a new row, or an
> > > > UPDATE for a second).
> > > >
> > > > What I often do in such situations is include a
> > > > hidden field in the input form that
> > > > says one of the following things:
> > > >
> > > > <input type="hidden" name="action"
> > > > value="Create">
> > > > <input type="hidden" name="action"
> > > > value="Delete">
> > > > <input type="hidden" name="action"
> > value="Edit">
> > > >
> > > > depending on which action the user originally
> > asked
> > > > for. That way, the action
> > > > class knows what to do, based on calling:
> > > >
> > > > request.getParameter("action")
> > > >
> > > > to see what was included in the form.
> > > >
> > > > For cases where the user doesn't select which
> > action
> > > > to perform until the form is
> > > > submitted, this field could be set in a
> > JavaScript
> > > > function, or be chosen by which
> > > > submit button was pressed.
> > > >
> > > > Craig McClanahan
> > > >
> > > >
> > >
> >
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