This method is called before the service invoked in change mode.
Input
Input/Output
Return value
PageBody or null - if a page body is returned, this is considered the result of the invocation and the underlying service will not be called. If null is returned, the underlying service will be invoked normally.
Throws
InteceptorError - throw this exception when an error occurs.
InterceptorWarning - throws this exception to signal an application warning