JZlib is no longer maintained, and continuing to carry a custom fork is a burden. I have found the Java 7+ GZIPInputStream and GZIPOutputStream classes to work well as a drop-in replacement. No open source Jenkins plugins still use these APIs. https://docs.cloudbees.com/docs/release-notes/latest/plugins/cloudbees-workflow-template-plugin/ and https://docs.cloudbees.com/docs/release-notes/latest/plugins/operations-center-clusterops-plugin/ still use GZIPInputStream, but those usages should be trivial to migrate.