Invoked by the ORB to dispatch a request to the servant.
ORB passes the method name, an InputStream containing the
marshalled arguments, and a ResponseHandler which the servant
uses to construct a proper reply.
Only CORBA SystemException may be thrown by this method.
The method must return an OutputStream created by the
ResponseHandler which contains the marshalled reply.
A servant must not retain a reference to the ResponseHandler
beyond the lifetime of a method invocation.
Servant behaviour is defined as follows:
1. Determine correct method, and unmarshal parameters from
InputStream.
2. Invoke method implementation.
3. If no user exception, create a normal reply using
ResponseHandler.
4. If user exception occurred, create exception reply using
ResponseHandler.
5. Marshal reply into OutputStream returned by
ResponseHandler.
6. Return OutputStream to ORB.
