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From Craig McClanahan <craig...@apache.org>
Subject Re: Theoretical debate
Date Fri, 09 Jul 2004 00:35:08 GMT
Hookom, Jacob wrote:

>Look at JSF, do you have actions? No, JSF just updates your POJO beans and
>calls methods on them.  Why have an ActionForm or have to create all of
>these Actions that are simply getter/setter adapters?  Please don't be too
>quick to retort to my supposed anti-struts mindset, but there are other
>frameworks out there that allow direct interaction with my business objects
>and don't require a heck of a lot of framework specific coding.
>
>  
>
(Coming into this discussion late, but figured that my experience on 
both the Struts and JSF side of things might provide some illuminating 
food for thought :-)

It's instructive, first, to go back to the beginning of Struts 
development (just over four years ago), and recall why an ActionForm 
exists in the first place.  The only reason we created that abstraction 
was to deal with some pesky real world problems in designing webapps ... 
primarily dealing with conversion (where we really punted ... see 
below), validation, and little things like maintaining the state of 
checkboxes.  Because Struts doesn't have any "user interface component" 
concept, dealing with those things had to go somewhere -- and a common 
abstraction at least made it easy to understand.

Therefore, the recommended design pattern for a Struts based app becomes:

- An ActionForm per input <form>, normally with
  String-based properties (so you can redisplay
  invalid input the way users expect you to).

- A set of validation rules that are applied for you
  on the server side, and optionally also on the
  client side.

- If a validation error occurs, Struts takes care
  of redisplaying the page (with error messages)

- If validation succeeds,  the application Action
  is responsibe for performing conversions of the
  String valued things in the ActionForm to match
  the underlying model data types, typically by
  copying them in to DTO/VO type objects and
  passing them to business logic (although, as others
  have pointed out, lots of Struts developers have
  skipped this extra layer).

With JSF, the component model takes care of all the responsibilities 
that Struts uses an ActionForm for, so you don't need one any more.  
Indeed, I anticipate people will choose one or more (they aren't 
mutually exclusive) of at least three different styles for building 
JSF-based webapps:

(1) You can bind individual *components* to backing bean properties,
     similar to how ASP.Net "code behind files" work.  This will
     be most comfortable to VB developers, and is useful when
     you need to programmatically modify component properties.

(2) You can bind component *values* directly to properties in your
     backing bean, and then provide the business logic as action methods
     in the same class.  Because the components take care of conversion,
     you're free to use model-oriented data types for such properties,
     so you don't need to worry about explicit conversion any more.
     This style will appear to Struts developers like a combination of an
     Action and an ActionForm in the same class, and will also appeal to
     the crowd that likes O-O encapsulation :-).

(3) You can bind component *values* directly to properties on a VO/DTO
     object, and bind action events to methods on a separate bean that will
     either perform the logic directly or delegate to a business logic 
class.
     This style will feel more like traditional Struts separated 
ActionForm and
     Action classes, but the Action won't have as much to do.  It's also 
a great
     way to build a webapp on top of existing application infrastructure 
that
     provides resuabe VO/DTO and business logic classes already.

I believe that all three approaches are valid -- which one you take for 
a particular application function depends on your use case for that 
function.  You don't have to be exclusive, either.  Combine them where 
it makes sense.

Craig McClanahan


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