How to modify the date validation in Struts?

[Thai Dang Vu]

Hello everybody,
 
I just tested the date validation in Struts and it seems to me that 12/31/2004 
is valid but 12-31-2004 is invalid. Where should I change so that 12-31-2004, 
Dec 31 2004 .... are valid?
 
Sincerely,
 
Thai