Converting various different date formats in to one common date format Java or Perl

Converting various different date formats in to one common date format
Java or Perl

I have huge set of data stored on server and it's different rows contain
dates in as many as 20+ different formats. I want to convert them in to
one common format. How can I achieve that? Do I need to write separate
function for each format or is there some super function which can read
date of any format and convert it to a specific format.