Separate client from server errors as much as possible in this order:
- raise MultipartException when resolving a multipart arg and the
request is not a multipart request (400)
- raise IllegalArgumentException when the arg type is MultipartFile
but the request is not of type MultipartHttpServletRequest (500)
- raise MissingServletRequestPartException when a MultipartResolver
is in use but the part is not found (400)
- detect presence of Servlet 3.0 before using standard multipart
parsing to find a request part or raise
IllegalArgumentException (500)
Unfortunately it is not always possible to separate client from
server errors mainly because the Servlet 3.0 API does not
distinguish between the case of 0 request parts vs multipart
processing not being configured.
Rossen Stoyanchev