I\'d like to know if there is a jar-file out there that could do the following:
DateMidnight dateInQuestion = new DateMidnight(12,12,2000);
DateChecker.isNat
I think you'll have to do the work yourself.
National holidays are determined by, well, nations. They can change, and are, by definition, not universal, and can thus not be captured by some algorithm.
The only way to keep track of them, is to maintain them on a per-nation basis.
Perhaps someone actually already does that (maybe a webservice of sorts), but I doubt it, to be honest.