grimepp_AntiBungeeHack.java

package me.grimepp;

import org.bukkit.ChatColor;
import org.bukkit.plugin.java.JavaPlugin;

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

public class AntiBungeeHack extends JavaPlugin {
    private static List<UUID> tempquit;
    private static List<String> ips;
    private static String ip;
    private static String kickmessage;

    public static String getKickmessage() {
        return kickmessage;
    }

    @Override
    public void onEnable() {
        saveDefaultConfig();
        tempquit = new ArrayList<>();
        ips = new ArrayList<>();
        ip = this.getConfig().getString("ip");
        kickmessage = ChatColor.translateAlternateColorCodes('&', this.getConfig().getString("kickmessage"));
    getServer().getPluginManager().registerEvents(new Event(), this);
    }

    public static List<String> getIps() {
        return ips;
    }

    public static List<UUID> getTempquit() {
        return tempquit;
    }

    public static String getIp() {
        return ip;
    }
}

grimepp_Event.java

package me.grimepp;

import org.bukkit.event.EventHandler;
import org.bukkit.event.EventPriority;
import org.bukkit.event.Listener;
import org.bukkit.event.player.AsyncPlayerPreLoginEvent;
import org.bukkit.event.player.PlayerLoginEvent;
import org.bukkit.event.player.PlayerQuitEvent;

import java.util.UUID;

public class Event implements Listener {
    @EventHandler
    public void onAsyncPlayerPreLoginEvent(final AsyncPlayerPreLoginEvent e) {
        try {
            if (AntiBungeeHack.getIps().contains(e.getAddress().getHostAddress())) {
                e.disallow(AsyncPlayerPreLoginEvent.Result.KICK_OTHER, "");
            }
        } catch (NullPointerException ignored) {
            e.disallow(AsyncPlayerPreLoginEvent.Result.KICK_OTHER, AntiBungeeHack.getKickmessage());
        }
    }

    @EventHandler(priority = EventPriority.HIGHEST)
    public void onJoin(PlayerLoginEvent e) {
        try {
            if (!e.getRealAddress().getHostAddress().equals(AntiBungeeHack.getIp())) {
                AntiBungeeHack.getIps().add(e.getAddress().getHostAddress());
                e.disallow(PlayerLoginEvent.Result.KICK_OTHER, AntiBungeeHack.getKickmessage());
                AntiBungeeHack.getTempquit().add(e.getPlayer().getUniqueId());
            }
        } catch (NullPointerException ignored) {
            e.disallow(PlayerLoginEvent.Result.KICK_OTHER, AntiBungeeHack.getKickmessage());
        }
    }

    @EventHandler(priority = EventPriority.MONITOR)
    public void onLeave(PlayerQuitEvent e) {
        UUID uuid = e.getPlayer().getUniqueId();
        if (!AntiBungeeHack.getTempquit().contains(uuid)) {
            AntiBungeeHack.getIps().remove(e.getPlayer().getAddress().getAddress().getHostAddress());
        } else {
            AntiBungeeHack.getTempquit().remove(uuid);
        }
    }
}

:O