Calendar 取上一年，上个月日期

        Calendar cal = Calendar.getInstance();
        cal.add(Calendar.MONTH,-12);//上一年
        //cal.add(Calendar.MONTH,-1);//上个月 
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        String day = sdf.format(cal.getTime());
        System.out.println(day);//2020-09-24