/**
     *
     * @param num ﹣3 三天前 +3 三天后
     * @return
     */
    public static String getDayAgoOrAfterString(int num){
        Calendar calendar1 = Calendar.getInstance();
        SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd");
        calendar1.add(Calendar.DATE, num);
        return sdf1.format(calendar1.getTime());
    }