Long warup time

Hi

I’m using small jruby app to convert odt to pdf using
http://www.artofsolving.com/opensource/jodconverter java library.
I’m using Java 1.6.0 and jruby 1.7.2. and jruby --server to start
app. With the first request the warm up time of the app is terrible
slow, so I get TimeoutError, after that next hits are successful.
Do you know what cause the long warmup time? (maybe class loading or
memory paging?) Can I preload all classes into memory so first hit
will not fail anymore?

best regards

Jakub