on 6/14/01 1:32 PM, "Peter Lynch" <[EMAIL PROTECTED]> wrote:
> Hi,
>
> Someone asked me why the need to separate action
> classes from screen class code. In other words, they
> were wondering why not have the screen classes do all
> the work? I was brain dead at the time so I think I
> did not give a very compelling argument why....
>
> So can anybody offer some compelling
> reasons/advantages for this design as opposed to
> having the screen classes do all the work of putting
> and getting?
>
> Thanks,
>
> Peter
MVC.
In other words, the conceptual model behind regular HttpServlets and JSP
pages is that you submit to the same page, put a big if-statement tree in
there and figure out what to do depending on what button was pushed. In
summary, that is a brain dead stupid model to use. The reason is simple: It
can be done better and easier.
Instead, it is better to section out the Controller and Model from the View.
In reality, these days, a properly designed application should never have
*any* Java Screen modules other than potentially a "Default.java" which gets
executed for every Screen template in a directory. This is called the Pull
Model.
So, what you are left with is Action modules. I developed the idea of
ActionEvents which is the concept of tying a <form> button to a method call
in an Action. This removes the need for a silly if-statement tree to figure
out which button was pressed. All you need to do is relate a Java method to
what is supposed to be executed with someone clicks a button. The cool thing
here is that, if you do it right, Actions are not tied to the template. You
can re-use an Action across several different pages. For example, if you
have a "Search" <input type="text"> field on several pages, you don't want
to have to copy/paste code into each and every Action that is supposed to
deal with it. Instead, you can make a single Action module and re-use that
on every screen or make a BaseAction, put your method in it and then have
whatever Actions you want extend it and get the functionality to be able to
handle the submit.
Things to read:
<http://jakarta.apache.org/turbine/pullmodel.html>
<http://jakarta.apache.org/turbine/howto/action-event-howto.html>
-jon
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