TPGUI.java

package com.dgrissom.tpgui;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.SkullType;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.inventory.InventoryClickEvent;
import org.bukkit.event.inventory.InventoryCloseEvent;
import org.bukkit.event.player.PlayerKickEvent;
import org.bukkit.event.player.PlayerQuitEvent;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.SkullMeta;
import org.bukkit.plugin.java.JavaPlugin;

import java.util.HashSet;
import java.util.Set;
import java.util.UUID;

public class TPGUI extends JavaPlugin implements Listener {
    private static Set<UUID> guisOpened = new HashSet<>();

    public static ItemStack getPlayerHead(Player player) {
        ItemStack head = new ItemStack(Material.SKULL_ITEM, 1, (short) SkullType.PLAYER.ordinal());
        SkullMeta meta = (SkullMeta) head.getItemMeta();
        meta.setOwner(player.getName());
        meta.setDisplayName(ChatColor.RESET + player.getName());
        head.setItemMeta(meta);
        return head;
    }

    public static Inventory getGUI(Player player) {
        Inventory inventory = Bukkit.createInventory(player, 9 * 6, "TPGUI"); // 6 rows
        for (Player p : Bukkit.getOnlinePlayers())
            if (!p.getUniqueId().equals(player.getUniqueId()))
                inventory.addItem(getPlayerHead(p));
        return inventory;
    }

    @Override
    public void onEnable() {
        Bukkit.getPluginManager().registerEvents(this, this);
    }

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        if (cmd.getLabel().equalsIgnoreCase("tpgui")) {
            if (!(sender instanceof Player)) {
                sender.sendMessage(ChatColor.RED + "Only players can run that command!");
                return true;
            }

            Player player = (Player) sender;
            guisOpened.add(player.getUniqueId());
            player.openInventory(getGUI(player));
            return true;
        }

        return false;
    }

    @EventHandler
    public void onInventoryClick(InventoryClickEvent evt) {
        Player player = (Player) evt.getWhoClicked();
        if (guisOpened.contains(player.getUniqueId())) {
            if (evt.getCurrentItem().getType() == Material.SKULL_ITEM) {
                SkullMeta meta = (SkullMeta) evt.getCurrentItem().getItemMeta();
                String owner = meta.getOwner();
                player.closeInventory();
                player.performCommand("tpa " + owner);
            }
        }
    }

    @EventHandler
    public void onInventoryClose(InventoryCloseEvent evt) {
        guisOpened.remove(evt.getPlayer().getUniqueId());
    }
    @EventHandler
    public void onPlayerQuit(PlayerQuitEvent evt) {
        guisOpened.remove(evt.getPlayer().getUniqueId());
    }
    // playerquit is not called when a player is kicked
    @EventHandler
    public void onPlayerKick(PlayerKickEvent evt) {
        guisOpened.remove(evt.getPlayer().getUniqueId());
    }
}