You can use Joda lib to convert Julian days to java date
DateTime dt = new DateTime(DateTimeUtils.fromJulianDay(2456324.5));
Julian date - number before decimal point represent number of days since noon on January 1, 4713 BC, and after decimal point fraction of the day; For example, the Julian Date for 1.1.2013 UT 0:30:00, is 2456293.520833