Although Corda is currently distributed as a JAR, this will change soon and we’ll be switching to distributing native executables on most platforms. Or at least on supported production platforms. That is, we will be providing a Linux ELF64 tarball that you extract and run.
Internally this will be an optimised and customised JVM, probably (once we switch to Java 9) built using the jlink tool. However, it means that the JVM version will be controlled by Corda itself and not the node operator. There are several reasons for this, but one of them is that the Java platform version is exposed as part of the Corda platform version. Thus, there must be consistency in what versions of the Java library apps can expect to have. Additionally, jlink allows for optimisation of the JVM install to that specific app, reducing memory usage, disk usage, startup time and CPU overheads. It’s the direction Java is heading in.