code: public void writeExternal(ObjectOutput out) throws IOException
     {
        if (url == null)
        {
           super.writeExternal(out);
           return;
        }
        out.writeInt(orderNumber);
  
        // write the path
        byte[] buf = url.toString().getBytes("UTF-8");
        out.writeInt(buf.length);
        out.write(buf);
     }
docs: {@inheritDoc}