MacOS – When try to I open a .jar I get “The java JAR file could not be opened”

Finally found it in System Preferences -> Users -> Login items.

Minecraft Server should be detectable through the arguments passed to its java process.

Over at Unix & Linux, the question kill process based on arguments tackles this problem: how to kill a specific java process based on its command line arguments.

The top answer recommends using pkill with the -f flag to kill based on the arguments associated with a specific process. The final command may be as simple as:

pkill -f 'MinecraftServer'

With regard to using cron, this is fine but Apple recommend migrating to launchd as cron is less efficient.