由给定日期获得前几个月日期

由给定日期取得前几个月日期
Integer i = 0;
     Integer j = 0;
     SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
     Calendar calendarStart = new GregorianCalendar();
     Calendar calendarEnd = new GregorianCalendar();
     String qdsjStart  = "";
     String qdsjEnd = "";
     try {
      calendarStart.setTime(sdf.parse(qdsj));
      calendarEnd.setTime(sdf.parse(qdsj));
     } catch (Exception e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
     }
     if("0".equals(sj)){//上半年价格变动
      i = -12;
      j = -6;
     }else if("1".equals(sj)){//下半年价格变动
      i = -6;
      j = 0;
     }else if("2".equals(sj)){//全年价格变动
      i = -12;
      j = 0;
     }
     calendarStart.add(calendarStart.MONTH, i);
     calendarEnd.add(calendarEnd.MONTH, j);
     qdsjStart = sdf.format(calendarStart.getTime());
     qdsjEnd = sdf.format(calendarEnd.getTime());
     if(qdsjStart!=null&&!"".equals(qdsjStart)){
      if(qdsjEnd!=null&&!"".equals(qdsjEnd)){
       hql += " and qdsj between '"+qdsjStart+"' and '"+qdsjEnd+"' ";
      }
     }