Obtain list of indexed fields from IndexWriter

[Ishan Chattopadhyaya <ic...@gmail.com>]

Hi,
If an update to a non-existent dv field is attempted, IndexWriter throws an
exception:
"can only update existing numeric-docvalues fields!".

This exception is thrown after checking with the globalFieldNumberMap
(which is obtained from the SegmentInfos).

Is there a way, given an IndexWriter instance, I can obtain a list of
fields that have been indexed through this writer (so that I can check
before attempting to update a non-existing DV field)? In absence of
something that I'm missing that exists already, is it possible to expose
either the segmentInfos or the globalFieldNumberMap as a public API?

Regards,
Ishan