得到前n天时间

private long getFetureDate(int past)  {

    Calendar calendar = Calendar.getInstance();
    calendar.set(Calendar.DAY_OF_YEAR, calendar.get(Calendar.DAY_OF_YEAR) - past);
    Date today = calendar.getTime();
    Log.e("TAG", "today="+today);
    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd 00:00:00");
    String result = format.format(today);
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    Date date = null;
    try {
        date = simpleDateFormat.parse(result);
    } catch (ParseException e) {
        e.printStackTrace();
    }
    long ts = date.getTime();
    Log.e("SUN", result);
    Log.e("SUN", ""+ts);
    return ts;
}