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.