Ingesting whole files

Looking for the best way to ingest whole files.
Potentially three outcomes would be of interest:
a) Ingest the whole plaintext file as a single-field document.
b) Ingest the file as k-v pairs (ini-style file).
c) Ingest XML file, parsing the nodes.

In each of these cases, looking for a way to re-read the whole file [if it has changed].

The attachment processor seems like an overkill, as it deals with binary files.

Found similar discussion topics, but didn't grasp how to achieve the desired outcome.

Are there "howtos for dummies" on such a setup?