A multi-version Java Docker Convenience Image would be very helpful.
If you e. g. want to build a multi-release JAR, you need to do some cross-compilation,as in compile 80% of the project with JDK 8 so that it is compatible with JDK 8 at runtimeand compile the JDK 9 specific parts with JDK 9, stuffing them in a multi-release JAR thatthen can work properly on both JDK 8 and JDK 9 with having JDK 9 specific stuff that is simply ignored for JDK 8.
It would require much CircleCI specific work to be done in the build to use workflows to do the JDK 9specific part in one image and move the result via workspace to the remaining tasks that can be donewith the JDK 8 image. It would be much easier, more convenient and used as is at the developerbox if there would be an image with both versions installed.
Of course I can either install the missing JDK or build a custom docker container with both Java version installed,but I think this could be a quite common requirement, so it might be feasible to also provide a pre-configuredconvenience image that contains multiple Java versions.