request header field name (case-insensitive; must be one of the message header field values of interest passed on instantiation)
integer value of the request header field
HeaderParameterException if - the field is missing in the header or - the field does not contain an unsigned integer value in decimal representation.
Obtains the integer value of the request header field corresponding to header_field_name. The header field value is expected to represent an unsigned integer number in decimal representation.