Let me know if I am not understanding. As I understand your question you…
Have a jar you are running directly.
Want this jar to be launched (as a daemon?) automatically on boot (act as a service)
You want the service to be triggered based on the runlevel reported by linux
- 3 Multi-User Mode with Networking Starts the system normally.
- 4 Undefined Not used/User-definable
- 5 X11 As runlevel 3 + display manager(X)
- 6 Reboot Reboots the system
I assume this means you want something to happen based on whether the server is in multi-user mode, single-user mode or in a Graphical X.org environment?
If that is the case, the current runlevel can be determined with the command
runlevel so you could pretty easily script different actions based on the runlevel. I’d be happy to help you put together a basic script if you can share a little more information on what outcome are looking for.