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From Werner Punz <werner.p...@gmail.com>
Subject Re: Tomahawk release plans?
Date Fri, 16 Mar 2007 13:49:28 GMT
Jörn Zaefferer schrieb:
> I'm not familiar with Velocity, therefore I'd like to know how velocity
> handles "logic" in its views. JSF in general does a good job avoiding
> any classic if/else and loop constructs in my views. Can I get that with
> Velocity, too?
> 
actually jsf tries to avoid it and then mixes it in again via helper
constructs (datalist in tomahawk or ui:repeat in facelets), thing is,
that a templating mechanism basically has the same
language needs as every other language, which is
sequences, iterations and selections!


JSF/EL follows the we want to be as minimalistic as possible approach
and fails so far that the core language constructs had to be added via
crude helper constructs.

Velocity is on the other side of the fence, it adds a full blown
language for templating which is as far as possible from xml to make a
visual difference in editing, but it still tries to keep a clear border
between model/controller and view.

So what you get is, a full blown language on its own, with macro
capabilities, an internal macro compiler and cacher, and still a clear
border which is needed in mvc (one of the reasons why JSP itself is a
bad solution is that it blurs those borders)

So a typical velocity construct looks like this

<h1>$component.myvalue</h1>

#if($compoment.myvalue == 'A')
   #macro1($component)	
#else
   <h2 styleClass="error"> component value is not set </h2>
#end


so where is the difference to the printwriter...

the difference is, basically an inversion of rendering,
you basically define the renderers in the language you want to target,
but with a full blown programming language underneath it which allows
encapsulation of code parts sequences and iterations, but the
strict cut between component as model/controller part is still there,
the code is just shifted into a domain which is easier to maintain, than

hundreds of lines of prints and calls into constants.
I personally see this approach more feasable than a crude
html/el approach or an approach of adding helpers ot the printwriter,
or even worse the introduction of another jsp layer onto the component
renderer where scriptlets are reintroduced again.


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