把20170909格式转成2017-09-09格式

1 SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
2                          SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd");
3                          startDate = sdf2.format (sdf.parse (startDate));;
4                          endDate = sdf2.format (sdf.parse (endDate));;
5                          result.put("startDate", startDate);
6                         result.put("endDate", endDate);