Multi-release JARs - Good or bad idea?

Multi-release JARs (MRJARs), introduced in Java 9, allow packaging multiple versions of the same class for different JVM runtimes in a single artifact. While they solve a real problem for library authors needing to support multiple Java versions, Gradle's team argues they are the wrong solution. Key criticisms include: mixing artifacts with different dependency trees into one JAR, breaking equivalence between consuming from a JAR vs. class directories, and hindering build parallelism. The preferred alternative is variant-aware dependency management with separate JARs per runtime target. Despite this stance, the post provides a complete Gradle setup for building MRJARs using source sets, cross-compilation, and forked test VMs for those who still need them.