public static String getRandomStringByLength(int length) {        String base = "0123456789";        Random random = new Random();        StringBuffer sb = new StringBuffer();        for (int i = 0; i < length; i++) {            int number = random.nextInt(base.length());            sb.append(base.charAt(number));        }        return sb.toString();    }    /**     * @function 生成商户订单号/退款单号     * @date 2015-12-17     * @return String     */    public static String getOrderNo(){        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmssSSS");        Date date = new Date();        return sdf.format(date) + getRandomStringByLength(4);    }