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Case Study: XMLC vs. Velocity

A while ago, a question was asked on a Jakarta Tomcat mailing list about XMLC and Velocity. Bojan Smojver gave this thoughtful reply, and gave us permission to present it here on the Velocity site.

I found this in the tutorial for XMLC:

XMLC is a Java-based compiler that takes a document written in the
Hypertext Markup Language (HTML) or the eXtensible Markup Language (XML)
and creates Java classes that will faithfully recreate the document. The
resulting Java classes can be used to insert dynamic content into the
document framework at run time. XMLC, therefore, is a wonderful way to
create dynamic HTML or XML documents from Java.

This sounds awfully like JSP to me, which is reason #1 why someone would
use Velocity.

Although I use Velocity for my web work, Velocity is a generic template
engine, it doesn't really care about the rest of the content. And that's

I use XSLT (sorry Jon, promise to give Anakia another look :-) to
prepare my documents from XML into XHTML (this is not done at run time,
not like Cocoon) and Velocity doesn't get upset much by that (except for
the fact that you can't have '&&' (VTL and) in XSLT without applying a
few tricks) but I've overcome that through Ant's nice replacement

Anyway, the first bad point to XMLC goes for the pains of code
generation, which Velocity avoids so neatly.

The second is the actual process of designing the complete solution
which is pictured here:

Designer designs the page and then engineer puts in the logic? This
sounds very bad to me. There should be a 'box full of Lego's' designers
can choose their functionality from, not the other way around. If
engineers have to be involved in simple projects, it comes back to
employing engineers to do everything in the first place. And why
wouldn't you use even JSP or ECS in such a case? You're are mucking
around with Java again... The XMLC cycle is just too long and it doesn't
make sense at all - what happens when a designer (by mistake or
intentionally) screws up the id's in the page? All of the engineers code
becomes unusable. Now that's a nice separation between presentation and

Second bad point.

An example from my 'production line', which illustrates how Velocity
handles the above. I have a few classes that handle all inquiry forms:
one class handles the fields from the form and stores those into a
database, the other one picks the fields and mails them to designated
e-mail address. These classes are beans and are loaded from the only
servlet I ever use (licensed GPL, but could contain any number of bugs
since I wrote it), which handles ALL Velocity pages: 331 lines long
including comments. Beans have scope and all, just like with JSP's.

Once the first ever form is created and debugged, an imaginary web
designer on my 'production line' would copy and existing Velocity page
from a previous project, change the fields (their names, their number...
whatever) in it and the other content. Once they post the page on the
site, that's it. It just works. They didn't even have to talk to an
engineer to get things done. Now that's MUCH better then XMLC!

I think the biggest problem XMLC, JSP and servlets are facing is more of
a philosophical nature: the document is data, not code - and Velocity
treats it exactly like that. Why would you convert your HTML into a Java
class when you want to send it to the browser as text?

My 2 cents. Velocity rocks!


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