You want DateTime::Format::Strptime.

#!/usr/bin/perl

use strict;
use warnings;

use DateTime::Format::Strptime;

my $date = '2005 322'; # 322nd day of 2005

my $p = DateTime::Format::Strptime->new(pattern => '%Y %j');

my $dt = $p->parse_datetime($date);

print $dt->epoch, "\n", $dt->dmy, "\n";
[download]

Oh, and by the way, what you have there is not really a Julian Day.