Bukkit

@Override
public static void onEnable() {
	getServer().getPluginManager().registerevents(this, this);
	config();
}
public static void playerDamage(PlayerDamageByProjectileEvent event) {  //put what you want for jumping damage (for a bit of a debuff for the awsomeness of jumping were you look)
if (hashmap.get(isJumping) == true) {
  if (event.getDamager() instanceof Arrow) {
    Int e = config.get("Config.damage");
     event.setDamage(e);
      Player player = event.getPlayer;
      player.setVelocity(player.getVelocity() - player.getVelocity());  //stop them when they are hit
      player.setFallDamage(0);
      hashmap.set("isJumping", false);
public static void playerleave(playerLeaveEvent event)
	if (hashmap.get(isJumping) == true) {
	     player.setFallDamage(0);
	     hashmap.set("isJumping", false); //make sure they dont die when leaving mid jump but still making them fall
}
}
}
}

	@Override
	public void onEnable() {
	HashMap<Player, Boolean> isJumping = new HashMap<>();
	getServer().getPluginManager().registerevents(this, this);
	config();
	}

	@Override
	public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) { //my imatation of your code :P
		if (cmd.getName().equalsIgnoreCase("launch")) { 
			Player player = event.getPlayer();
			Vector direction = player.getDirection.getVelocity();
			player.setVelocity(direction);
			HashMap.put(event.getPlayer(), true);
			return true;
		}
        
		return false; 
	}

	public static void launch (Player player) { //player player is the modifiers which mean that when the api's user does launch.player(); they can fire the player that they get
		Player player = event.getPlayer();
		Vector direction = player.getDirection.getVelocity();
		int speed = config.get("Config.speed");
		player.setVelocity(direction * speed);
}
	public void playerfalldamage (EntityDamageEvent event) {
		 if(event.getEntity() instanceof Player && event.getCause() == DamageCause.FALL) { //this part may not work figure it out yourself like i said im not coding for you
			if(hashmap.get(event.getPlayer() == true) {
			hashmap.set(event.getPlayer(), false);
			event.setCanceled(true); //cancel there fall damage and make sure the api user doesnt think the player is still in the air
			
}
}
} 	public static void onPlayerJoinEvent(onPlayerJoinEvent event) {
	hashmap.put(event.getPlayer(), false);	
} 
	public static void config() {
  		saveConfig();
		FileConfiguration config = getConfig();
		config.addDefualt("Config.speed", 2);
		config.addDefualt("Config.damage", 2);

} 
		
}