//向前推的天数
     public String afterDate(int days) {
        String dt = "";

        try {
            Calendar cal = Calendar.getInstance();
            cal.setTime(new Date());
            cal.add(Calendar.DATE, - days);   //向前推的天数
            SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
            dt = format.format(cal.getTime());
        } catch (Exception e) {
            e.printStackTrace();
        }

        return dt;
    }

    //计算相差天数
    public int countDays(String time1,String time2) {
        int days = 0;

        DateFormat df = new SimpleDateFormat("yyyy-MM-dd");
        Calendar c_b = Calendar.getInstance();
        Calendar c_e = Calendar.getInstance();

        try {
            c_b.setTime(df.parse(time1));      //转型为 yyyy-mm-dd
            c_e.setTime(df.parse(time2));

            while (c_b.before(c_e)) {
                days++;
                c_b.add(Calendar.DAY_OF_YEAR, 1);
            }

        } catch (ParseException pe) {
//            System.out.println("日期格式必须为：yyyy-MM-dd；如：2010-4-4.");
        }

        return days;
    }