Hi,
actually you can try to parse the date you retreived from the excel file, if the parse is done successfully the format will be ok. and if not an exception will raise so you can handle it.
example:
try{
DateFormat formatter = new SimpleDateFormat("dd/mm/yy");
Date date = (Date)formatter.parse("01/03/02"); // pass here the string retreived from excel as date
} catch (ParseException e) {
//Your code for handling date format error
}