I just went digging a bit for java id3 libraries.
The ones which sound best to me and are still active are jaudiotagger and entagged:
-
https://jaudiotagger.dev.java.net/
-
Entagged | Developer
The License is LGPL in both cases, so they can be used directly.
I didn't list myID3, as its license (Apache) might conflict mith the GPlv2 - to be able to use it, Phex might have to switch to using the GPLv3 which add compatibility to the Apache license.