In the same way you would invoke any other web service - using the SAAJ or JAX-RPC APIs. The beauty of web services is that it doesn't matter which language they're written in. I'd like to point out that it is considered bad design to have WS calls in a JSP page. you should move those to a servlet, and forward to a JSP after completion.
The glass is neither half full or half empty. It is too big. But this tiny ad is just right: