1.12.2 How can I use stuff in 'net.minecraft.server.v1_12_R1' across different versions?

Youll need to create a class that handles all the different version (since class path and methods are changed almost every version)

 

String test = "net.minecraft.server." + Bukkit.getServer().getVersion(); + "any else.."

try this

 

You'll either have to use reflection or separate gradle/maven modules to import multiple jars. If you want to go the multiple modules route, you can look at the HolographicDisplays repository for a little guidance: https://github.com/filoghost/HolographicDisplays/tree/master/NMS

 

This will also work, but some methods or variables name will be different based on the version.

 

i know

 

Good youtube tutorial:

Some threads about it:
https://www.spigotmc.org/wiki/nms-on-different-versions-without-reflection/
https://bukkit.org/threads/support-multiple-minecraft-versions-with-abstraction-maven.115810/
You could also use reflection as it's way easier to maintain, but it's also a good amount slower than abstraction