OpenJDK is open source community driven JDK which is deployed by customers to run their Java server applications. AMD has checked-in changes to OpenJDK which makes it to generate right an optimized code for EPYC processors from AMD. This will be available from OpenJDK 10 onwards, however, Java by nature does not have huge impact with specific code generation for X86 architectures. So, it should be ok to use JDK9 (or earlier versions) for your Java server applications.
