1.12.2 How to make firework explode where I stand?

Hello, I wonder how can I make so when I join (or where I will use this cosmetic feature) the firework would explode right where I stand and I could see the effect without turning to the air instead of it shooting up and exploding at a certain point? Maybe I shouldn't even use firework summoning but rather I should summon the effect itself? If so how?

Code:

Code (Java):

package net.hexilion.Basics.Events;

import net.hexilion.Basics.Items.SuperSword;
import org.bukkit.Color;
import org.bukkit.FireworkEffect;
import org.bukkit.Location;
import org.bukkit.entity.EntityType;
import org.bukkit.entity.Firework;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.inventory.meta.FireworkMeta;

import static org.bukkit.ChatColor.*;

public class Join implements Listener
{
    public String prefix = (AQUA + "" + BOLD + "   +  ");
    private SuperSword item = new SuperSword();
    @EventHandler
    public void onJoin(PlayerJoinEvent event)
    {
        Player player = event.getPlayer();
        event.setJoinMessage("");
        player.sendMessage(prefix + GREEN + "Welcome back, " + GRAY + player.getName() + GREEN + "!");
        item.giveItem(player);
        Location spawn = new Location(player.getWorld(), -212.5, 91, 445.5);
        player.teleport(spawn);
        if(player.hasPlayedBefore())
        {
            Location fireworkloc = spawn.clone();
            fireworkloc.subtract(0, 0, 0);//this doesn't do the job...
            Firework firework = (Firework) player.getWorld().spawnEntity(fireworkloc, EntityType.FIREWORK);
            FireworkMeta fireworkmeta = firework.getFireworkMeta();
            FireworkEffect.Builder builder = FireworkEffect.builder();
            fireworkmeta.addEffect(builder.flicker(true).withColor(Color.BLUE).build());
            fireworkmeta.addEffect(builder.trail(true).build());
            fireworkmeta.addEffect(builder.withFade(Color.RED).build());
            fireworkmeta.addEffect(builder.with(FireworkEffect.Type.CREEPER).build());
            fireworkmeta.setPower(0);//maybe here is the thing I need to change?
            firework.setFireworkMeta(fireworkmeta);
        }
    }
}

 

*bump*

 

I haven't use Runnable before could you give me an example of how it works or if possible what exactly I need to type in my code?

 

Also I have this issue where I cannot see explosion on my alt when I test only tail of firework, but I can see on account I join with(and for which the explosion is for)