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Posted to user@velocity.apache.org by Nick Bauman <ni...@cortexity.com> on 2001/07/25 22:08:23 UTC
Velocity mini case study

I just wanted to share my findings on Velocity. I use velocity as an
embedded mail templating system in our application server.

When I began this subproject, I was using JSP as the language for generating
template output for our application server. It was horrible. There were many
problems, not to mention the difficulty of embedding a servlet engine in the
app server that I could communicate with through direct method calls instead
of over a socket. Specific to the Velocity argument was the JSP template
versus the VTL template. I'd like to show you what my JSP template looked
like. Package names have been changed to protect the innocent. Here is an
example:

----------------8<---------------

<%@ page session="false"
        import="java.util.*,
        foo.events.*,
        foo.emeeting.*,
        foo.validation.*,
        foo.util.actionevent.ActionEvent,
        java.util.Date"%>

<jsp:useBean id="meeting" scope="request" type="foo.IMeeting"
class="foo.Meeting"/>

<html>

<!-- etc -->

<table width="600" border="0" cellspacing="0" cellpadding="4" bgcolor="white">
<tr>
<td>
<%
Iterator            events = meeting.getStoredEventsIterator();
int                 repId = 0;

%>
<i><b>Topic: <%= meeting.getTopic()%></b></i>
<p>
<%
while (events.hasNext()) {
  Object event = events.next();
  Participation yapper =
meeting.getParticipation(((MeetingEvent)event).getFromId());
  if(event instanceof ChatEvent) {
    if("R".equals(yapper.getRole()) ) {
%>
<font color="#000000"><b><%=yapper.getName()%>:</b></font>
<%
      repId = yapper.getParticipantId();
    } else {
%>
<font color="#0000f0"><b><%=yapper.getName()%>:</b></font>
<%
    }
    ChatEvent ce = (ChatEvent) event;
%>
<br>
<%
  } else if(event instanceof URLPushedEvent) {
    if("R".equals(yapper.getRole()) ) {
%>
<font color="#000000"><b><%=yapper.getName()%>:</b></font>
<%
    } else {
%>
<font color="#0000f0"><b><%=yapper.getName()%>:</b></font>
<%
    }
    URLPushedEvent pe = (URLPushedEvent) event;
%>
<a href="<%=pe.getStoredData()%>">"<%=pe.getStoredData()%>"</a> <br>
<%
  }
}
%>
<hr>
<br><%=meeting.getMeetingId()%>:<%=repId%><br>
</td>
</tr>
</table>
</div>
</body>
</html>

----------------8<---------------

Seasick yet? Now here is the Velocity template accomplishing the same thing
as above:

----------------8<---------------

<html>

<!-- etc -->

<table width="600" border="0" cellspacing="0" cellpadding="4" bgcolor="white">
<tr>
<td>
<i><b>Topic: $meeting.getTopic()</b></i><p>

#foreach( $event in $meeting.getStoredEventsIterator() )
  #set( $yapper = $meeting.getParticipation($event.getFromId()) )
  #if( $event.getClass().getName().equals($urlEvent) )
    #if( $repRole.equals($yapper.getRole()) )
      #set( $repId = $yapper.getParticipantId() )
      <font color="$blk"><b>$yapper.getName()</b></font>
    #else
      <font color="$blu"><b>$yapper.getName()</b></font>
    #end
    <a href="$event.getStoredData()">$event.getStoredData()</a> <br>
  #elseif( $event.getClass().getName().equals($chatEvent) )
    #if($repRole.equals($yapper.getRole()) )
      #set( $repId = $yapper.getParticipantId() )
      <font color="$blk"><b>$yapper.getName()</b></font>
    #else
      <font color="$blu"><b>$yapper.getName()</b></font>
    #end
    $event.getStoredData() <br>
  #end
#end
<hr>
<br>$meeting.getMeetingId():$repId<br>
</td>
</tr>
</table>
</div>
</body>
</html>

----------------8<---------------

I was subsequently able to define that largish foreach loop into a macro and
shrink it even more, using Velocity's #macro function, so I could do this:

#drawStandardHtmlTranscript ( $meeting )

removing 20 lines of code from each template whilst only adding 2 lines (one
for #parse and the other for the #drawStandardHtmlTranscript.

The call to the Velocity runtime to finally merge the template consumes
about 20-50 milleseconds (on a 400 mHz PII Linux system) when I pool the
contexts (time doubles when I do not). This is great performance, too!

Last but not least, teaching the web design team to write a template took
literally 10 minutes from start to finish. They haven't asked me a single
question since.

-- 
Nick Bauman
Software Engineer
3600 Dupont
Minneapolis, MN
55412
Mobile Phone: (612) 810-7406
Home Phone: (612) 522-0165