Is there a free open source Java library for checking ASN.1 BER / DER / XER on module definition files .
Yes, there is (usually this is part of the encoder / decoder library), for example:
JAC (Java Asn.1 Compiler) is a tool for you if you want (1) to parse your asn1 file (2), create .java and (3) encode / decode instances of your classes.
I think you could use some BouncyCastle Classes to create this function. Something that may also be useful: BERViewer