code: public static String toSortString(final List<Order> orders) {
      if (null == orders || orders.isEmpty()) { return ""; }
      final StringBuilder buf = new StringBuilder("order by ");
      for (final Order order : orders) {
        if (order.isAscending()) {
          buf.append(order.getProperty()).append(',');
        } else {
          buf.append(order.getProperty()).append(" desc,");
        }
      }
      return buf.substring(0, buf.length() - 1).toString();
    }
docs: <p>
  toSortString.
  </p>
  
  @param orders a {@link java.util.List} object.
  @return a {@link java.lang.String} object.