How to use (NBTs) - acrylic-style/NMSAPI GitHub Wiki
This page will introduce how to use NBT classes.
From ItemStack
import xyz.acrylicstyle.minecraft.utils.NBTUtils;
import org.bukkit.Material;
import org.bukkit.inventory.ItemStack;
import java.util.UUID;
...
ItemStack item = new ItemStack(Material.STONE);
NBTUtils tag = NBTUtils.load(item);
tag.setString("uuid", UUID.randomUUID().toString());
tag.save(item);
From Entity
import xyz.acrylicstyle.minecraft.utils.NBTUtils;
import org.bukkit.Bukkit;
import org.bukkit.entity.Player;
import java.util.UUID;
...
Player player = Bukkit.getPlayer("i want to die");
NBTUtils tag = NBTUtils.load(player);
tag.setString("unknownTag", UUID.randomUUID().toString());
tag.save(item);