Quando la data non si comporta come ti aspetti!

When displaying dates, the java.util package automatically adjusts for the local timezone. This can cause problems when displaying dates within an application, as the dates look as if they are exactly one day previous to that which is stored in the Excel spreadsheet, although this is not in fact the case.

Excel stores dates as a numerical value, and the conversion process for transforming this into a java.util.Date consists of converting the Excel number into a UTC value and then using the UTC number to create the java Date. Say the number in Excel represents 20 August 2003, then the UTC equivalent of this number is used to create a java.util.Date object.

The problem occurs if you are operating in a timezone other than GMT. As soon as you try and perform any user IO on that java Date object (eg. System.out.print(date)) the JVM will perform timezone adjustment calculations. If you are located in EST zone (which is GMT - 5 hours) java will subtract 5 hours from the date - so the Date object instead of being 00:00 20/08/2003 becomes 19:00 19/08/2003. Because java recognizes you only want a date and not a date time, it truncates the hours/minutes/seconds and presents 19/08/2003 - so it appears that the day is one day less than was stored in Excel, whereas it is really only a few hours (the timezone offset) less. Needless to say, this is a very annoying feature.

The easiest way to work around this (and the method used internally by the getContents() method of a jxl.DateCell) is to force the timezone of the date format as follows:
TimeZone gmtZone = TimeZone.getTimeZone("GMT");
SimpleDateFormat format = new SimpleDateFormat("dd MMM yyyy");
format.setTimeZone(gmtZone);

DateCell dateCell = ....
String dateString = format.format(dateCell.getDate());