James, I would highly recommend using SOAP-style communication (pure HTTP requests inbound to the servlet and XML returned from the servlet).
Firstly, you'll find it much easier to maintain the code on both sides of the communication stream; secondly, any platform can call these servlets and get useful results back (e.g., Perl, a mainframe, whatever).
We're using this approach in several big companies and it has been highly successful because it is language- and platform-independent. Just my 2c.
Dave
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