IBM did a partial implementation of ASN.1 in Java, and released it via the IBM AlphaWorks open-source repository. I used it in a telecommunications system in the 90s. Luckily the GSM protocol we were interfacing with only used a small subset of ASN.1, which was covered by the IBM software. IBM AlphaWorks is still online : https://www.ibm.com/support/pages/aix-toolbox-open-source-so... but only lists libtasn1, which is in C.

Here's a post about AlphaWorks : https://www.cnet.com/tech/services-and-software/ibm-alphawor...

Searching for that, I found this post, https://stackoverflow.com/questions/37056554/opensource-java... which mentions : https://www.beanit.com/asn1/ https://sourceforge.net/projects/jac-asn1/ which are more recent java ASN.1 implementations.