just for my understanding: This servlet does not use any extension? What mime-type do you send?
Can you try and add the extension ".json" to the servlet and use the appropriate mimetype for JSON?
Additional recommendation: Please bind your servlet to a resource instead to a harcoded path, and use a selector for selection. Because then you don't need to pass any path as query string to it, but whenever the servlet is invoked only if the resource is available.
Jörg
