DatePickerDialog 显示方式是MMDDYYYY ，如何改成YYYYMMDD
http://stackoverflow.com/questions/14190968/android-format-date-to-mm-dd-yyyy-from-datepicker
http://stackoverflow.com/questions/7208769/android-how-to-change-the-datepicker-view-date-format-from-mm-dd-yyyy-to-dd-mm