We have several additions to jPOS (see https://github.com/jpos/jPOS/wiki/ChangeLog).
In particular the CheckFields participant could be useful and we expect to add support for more fields and validations.
It’s documented in http://jpos.org/doc/proguide.pdf section 9.8 (Transaction Participants). You may also want to take a look at chapter 10 that documents the new org.jpos.rc package.
See https://github.com/jpos/jPOS/commits/master for details.