I'm trying to build a jar file for my Java program that depends on Skija with the help of the Gradle Shadow plugin. It builds fine, however, I can't run it, because it complains that sun.misc.Cleaner, referenced in Cleanable.java, doesn't exist. I can see that there are 2 versions of Cleanable.java, pre- and post-Java 9, and it looks like the pre-java-9 version ends up being used even though my JDK is newer.

What's the best strategy to create a working Jar file then? I'd be fine with one that doesn't work on Java versions before 9.