Villager trading screen plugin in scala!

package me.jtjj222.scalatest

import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.command.CommandSender;
import org.bukkit.command.Command;
import org.bukkit.Material;
import org.bukkit.entity.Player;
import org.bukkit.craftbukkit.entity.CraftPlayer;

import net.minecraft.server.EntityPlayer;
import net.minecraft.server.Packet250CustomPayload;
import net.minecraft.server.Packet100OpenWindow;
import net.minecraft.server.MerchantRecipeList;
import net.minecraft.server.MerchantRecipe;
import net.minecraft.server.ItemStack;

import java.io.DataOutputStream;
import java.io.ByteArrayOutputStream;
import java.util.logging.Level;

class ScalaPlugin extends JavaPlugin{

    override def onCommand(sender : CommandSender, cmd : Command, label : String, args : Array[String]):Boolean = {

     var player : CraftPlayer =
       sender match{
        case p : Player => p.asInstanceOf[CraftPlayer]
        case _ => {
          sender.sendMessage("This command can only be used by players, sorry!");
          return true;
        }
      }

      var packet = new Packet100OpenWindow(100,6,"",1);
      var recipes = new MerchantRecipeList;

      recipes.a(new MerchantRecipe(new ItemStack(Material.GLASS.getId(),1, 0), new ItemStack(Material.STONE.getId(),2,0), new ItemStack(Material.THIN_GLASS.getId(),3,0)));
      recipes.a(new MerchantRecipe(new ItemStack(Material.GLASS.getId(),1, 0), new ItemStack(Material.GLASS.getId(),20,0)));

      player.getHandle().netServerHandler.sendPacket(packet);

      var buffer = new ByteArrayOutputStream;
      var out = new DataOutputStream(buffer);

      //note exception catching is optional :D
      out.writeInt(100);
      recipes.a(out);
      player.getHandle().netServerHandler.sendPacket(new Packet250CustomPayload("MC|TrList", buffer.toByteArray()));

      return true;
    }
}