My suggestion would be to start with plain Java classes that call a JINI service. Only after you have that working should you attempt to integrate your working classes into a web application. Trying to do it all in one step leads to hard to debug mystery errors.
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com
subject: Calling JINI service from web application