Created attachment 23853 [details]
Patch to XSSFWorkbook.java from poi 3.5-beta6

When I create a spreadsheet using XSSFWorkbook with date values in them, and open the file on Mac Excel 2008, all of the date values are off by exactly 4 years.  I have done some investigation, and I believe the issue is due to differing defaults when the workbook.xml file has a missing <workbookPr> tag (which seems to happen with all xlsx files created via XSSFWorkbook).  According to the ECMA-376 docs, on page 2292, it talks about "1900" vs "1904 backward compatibility" for dates in xlsx files, and I believe the "lack" of a <workbookPr> tag showing the different defaults for Windows Excel 2007 and Mac Excel 2008.

If I simply add the following code after workbook creation, the <workbookPr> tag is added to the workbook.xml file, and the dates show properly on Mac Excel 2008, and Windows Excel 2007.

import org.openxmlformats.schemas.spreadsheetml.x2006.main.CTWorkbookPr;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

XSSFWorkbook workbook = new XSSFWorkbook();
if (workbook.getCTWorkbook().getWorkbookPr() == null) {
  // this code causes a <workbookpr> element to be written to the workbook.xml 
  // file.  If this mode isn't set, then Mac
  // Excel 2008 defaults to date1904 mode whereas Windows Excel 2007  
  // defaults to date1900 mode.
  CTWorkbookPr workbookPr = CTWorkbookPr.Factory.newInstance();
  workbookPr.setDate1904(false);
  workbook.getCTWorkbook().setWorkbookPr(workbookPr);
}


I will attach some screenshots and example code showing the differences between display of dates on Excel 2007/Excel 2008.  Also, I believe the patch to this is simply adding extra initialization to onWorkbookCreate() in XSSFWorkbook.java.  I will also attach a patch showing this addition.

Thanks much!
--Leif