java获取前一天，一周，一个月的时间区间

SimpleDateFormat  sdf = new SimpleDateFormat("yyyy-MM-dd");Date dateNow = new Date();Calendar cl = Calendar.getInstance();cl.setTime(dateNow);//cl.add(Calendar.DAY_OF_YEAR, -1);//一天//cl.add(Calendar.WEEK_OF_YEAR, -1);//一周//cl.add(Calendar.MONTH, -1);//一个月Date dateFrom = cl.getTime();System.out.println(sdf.format(dateFrom)+"到"+sdf.format(dateNow));