Java POI the supplied data appears to be in the Office 2007+ XML

I was using XSSF with a xlsx file, but got this error when I tried to process a file that was encrypted/protected with a password.

Once I removed the password, everything worked as expected.

According to the Apache POI Quick Guide, the POIFSFileSystem (or similarly, NPOIFSFileSystem) is only used with .xls (Excel versions through 2003) documents.

The equivalent for .xlsx documents (Excel 2007+) is OPCPackage.

OPCPackage pkg = OPCPackage.open(new File("file.xlsx"));

You can create an XSSFWorkbook from the OPCPackage:

XSSFWorkbook wb = new XSSFWorkbook(pkg);

Or you can just create it directly:

XSSFWorkbook wb = new XSSFWorkbook(new File("file.xlsx"));

Generally it's better to create the workbook using a File instead of an InputStream, to save memory.

Also, if you want code that doesn't care whether it's an .xls or an .xlsx:

// or "file.xlsx"
Workbook wb = WorkbookFactory.create(new File("MyExcel.xls"));