* Controller implementation that allows multiple request types to be
* handled by the same class. Subclasses of this class can handle several
* different types of request with methods of the form
*
* <pre>
* ModelAndView actionName(HttpServletRequest request, HttpServletResponse response);</pre>
*
* May take a third parameter HttpSession in which an existing session will be required,
* or a third parameter of an arbitrary class that gets treated as command
* (i.e. an instance of the class gets created, and request parameters get bound to it)