Fly on Join source

import org.bukkit.Bukkit;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.plugin.java.JavaPlugin;

public class Main extends JavaPlugin implements Listener {

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

    @EventHandler
    public void onPlayerJoinEvent(PlayerJoinEvent e) {
        Player player = e.getPlayer();
        if (player.isFlying()) {
            return;
        }
        if (!player.isFlying()) {
            player.setAllowFlight(true);
            player.setFlying(true);
            player.setFlySpeed(1f);
        }
    }
}