In my last project I had to parse the date but format was not fixed. I have googled for the same and found that grails 2.x.x added a new method in params using that you can parse the date regardless format. Code looks like :

def date='myDate', 'dd-MM-yyyy')
def'myDate', ['yyyy-MM-dd', 'yyyyMMdd', 'yyMMdd'])
//the format read from via the key 'date.myDate.format'

Note : This method of parsing only works inside a controller.
Hope this will help.