Packet failed to send to server

package advancedscience.core;

import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;

import net.minecraft.client.entity.EntityClientPlayerMP;
import net.minecraft.entity.player.EntityPlayerMP;
import net.minecraft.network.packet.Packet250CustomPayload;
import net.minecraft.world.World;
import cpw.mods.fml.common.FMLCommonHandler;
import cpw.mods.fml.common.network.PacketDispatcher;
import cpw.mods.fml.relauncher.Side;

public class PacketGui{
    public PacketGui(int xCoord, int yCoord, int zCoord, String action){

        ByteArrayOutputStream bos = new ByteArrayOutputStream(8);
        DataOutputStream outputStream = new DataOutputStream(bos);
        try {
                outputStream.writeInt(xCoord);
                outputStream.writeInt(yCoord);
                outputStream.writeInt(zCoord);
                outputStream.writeUTF(action);
        } catch (Exception ex) {
                ex.printStackTrace();
        }

        Packet250CustomPayload packet = new Packet250CustomPayload();
        packet.channel = "DanielScienceGui";
        packet.data = bos.toByteArray();
        packet.length = bos.size();

        PacketDispatcher.sendPacketToServer(packet);
    }
}