There have been a bunch of fixes to the #Java JDK! The JDK itself should now be reproducible (included in the JDK 19+21 early-access builds, JDK19 becoming generally available Sept 20th).
This also means any Java application should have an easier time building reproducibly.
https://bugs.openjdk.java.net/browse/JDK-8284539?jql=labels%20%3D%20reproducible-build