[Howto] use with varReader to import/parse large XML file ?

[smallufo]

In JSTL in Action page 336, 
Shawn demonstrated varReader attribute in <c:import> tag.

I have a big XML file (about 500Kbytes) ,
while using general 
<x:parse var="doc">
 <c:import url="/xxx.xml"/>
</x:parse>
<x:out select="$doc//xxx"/>
It costs a lot of time (about 12~14 seconds) to select nodes.

I wonder if varReader can improve the efficiency, I tried but cannot find how to 
combine varReader with XML parsing, can somebody give me a demonstration ?