A convenience method to write this uploaded item to disk.
This method is not guaranteed to succeed if called more than once for
the same part. This allows a particular implementation to use, for
example, file renaming, where possible, rather than copying all of the
underlying data, thus gaining a significant performance benefit.
fileName - The location into which the uploaded part should
be stored. The value may be a file name or a path. The actual
location of the file in the filesystem is relative to MultipartConfigElement.getLocation(). Absolute
paths are used as provided and are relative to
getLocation(). Note: that this is a system
dependent string and URI notation may not be acceptable on all
systems. For portability, this string should be generated with
the File or Path APIs.
Returns the value of the specified mime header
as a String. If the Part did not include a header
of the specified name, this method returns null.
If there are multiple headers with the same name, this method
returns the first header in the part.
The header name is case insensitive. You can use
this method with any request header.