MutableSortDefinition unable to sort dates

[Anonymous]

Hi
I have been using the sorting feature for string data as below
((MutableSortDefinition) holder.getSort()).setProperty(req.getParameter("sortOn"));           
((MutableSortDefinition) holder.getSort()).setToggleAscendingOnProperty(true);
holder.resort();

But when i use the same for dates it is not working could any one give an example how to implement the same for dates?

Thanks