Codec s that uses the MIME multipart as the underlying format.
When the runtime needs to dynamically choose a
Codec , and
when there are more than one
Codec s that use MIME multipart,
it is often impossible to determine the right
Codec unless
you parse the multipart message to some extent.
By having all such
Codec s extending from this class,
the "sniffer" can decode a multipart message partially, and then
pass the partial parse result to the ultimately-responsible
Codec .
This improves the performance.
author: Kohsuke Kawaguchi