메인클래스에 온조인

package com.first.testpl;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.craftbukkit.v1_12_R1.entity.CraftPlayer;
import org.bukkit.entity.Player;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.plugin.java.JavaPlugin;

import net.minecraft.server.v1_12_R1.PacketPlayOutTitle;
import net.minecraft.server.v1_12_R1.IChatBaseComponent.ChatSerializer;
import net.minecraft.server.v1_12_R1.PacketPlayOutTitle.EnumTitleAction;

public class Main extends JavaPlugin implements Listener{
    @Override
    public void onEnable(){
        Bukkit.getConsoleSender().sendMessage(ChatColor.BLUE + "플러그인이 활성화 되었습니다.");
        getCommand("test").setExecutor(new Cmd());
        getCommand("test2").setExecutor(new Cmd());
        getServer().getPluginManager().registerEvents((Listener) this, this);

    }

    @Override
    public void onDisable(){
        Bukkit.getConsoleSender().sendMessage(ChatColor.RED + "플러그인이 비활성화 되었습니다.");
    }

        public void onJoin(PlayerJoinEvent event){
            Player player = event.getPlayer();
            PacketPlayOutTitle title = new PacketPlayOutTitle(EnumTitleAction.ACTIONBAR,
            ChatSerializer.a("{\"text\":\"§a안녕하세요.\"}"),100,20,20);
            ((CraftPlayer) player).getHandle().playerConnection.sendPacket(title);
        }
    }