you can use the validator.xml
and for to arriave at your desired date format use the following piece of code which you can define your date format
date - validates that a field can be converted to a Date. This validation rule uses java.text.SimpleDateFormat to parse the date and optionally either a datePattern or datePatternStrict variable can be used. If no
pattern is specified the default short date format is assumed. The difference between using the datePatternStrict and datePattern variables is that datePatternStrict checks additionally that the input data is the same length as the pattern specified (so for example 1/1/2004 would fail with a pattern of MM/dd/yyyy).
<field property="saledate" depends="required,date">
<arg0 key="myForm.saledate"/>
<var><var-name>datePattern</var-name><var-value>MM/dd/yyyy</var-value></var>
</field>
<field property="saledate" depends="required,date">
<arg0 key="sale.orderdate"/>
<var><var-name>datePatternStrict</var-name><var-value>MM/dd/yyyy</var-value></var>
</field>
in the depends field you can have your own defined java script functions to validate the date.