PlayerAntiMerge.java

import java.util.List;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerDropItemEvent;
import org.bukkit.event.player.PlayerPickupItemEvent;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;

/**
 * Lead Developers:
 * CFerg | Elite
 *
 */
public class PlayerAntiMerge implements Listener{

    @EventHandler
    public void onDrop(PlayerDropItemEvent e){
        String user = e.getPlayer().getUniqueId().toString();
        
        ItemStack dropItem = e.getItemDrop().getItemStack();
        ItemMeta dropItemMeta = dropItem.getItemMeta();
        List<String> dropItemLore = dropItemMeta.getLore();
        
        dropItemLore.add(user);
        dropItemMeta.setLore(dropItemLore);
        dropItem.setItemMeta(dropItemMeta);
    }
    
    @EventHandler
    public void onPickup(PlayerPickupItemEvent e){
        ItemStack pickupItem = e.getItem().getItemStack();
        
        if (pickupItem.hasItemMeta()){
            ItemMeta pickupItemMeta = pickupItem.getItemMeta();
            List<String> pickupItemLore = pickupItemMeta.getLore();

            int end = pickupItemLore.size();
                
            pickupItemLore.remove(end);
            pickupItemMeta.setLore(pickupItemLore);
            pickupItem.setItemMeta(pickupItemMeta);
        }
    }
}