Hi,
First of all, I have to say there is a search engine described in Pro Java 
Server Programming (Wrox) using servlets, though it would need a bit of 
work (on threads) for live operation. This would turn over to JSP nicely. 
The point re. platform is a good one - I spent *ages* putting together a 
Java search engine on a Novell (Novonyx) network, before I released that 
there was a search engine already built in (RTFM!). I would also like to 
ask what kind of number of pages you wish to index? If there are only a few 
'significant' ones, where you don't need a spider/crawler and don't mind 
inputting the entries manually, then somewhere I've Javascript that will do 
this.

Cheers,
Danny.