Reading XLSM custom Properties

[Thomas P Laford]

I have the following code to read the custom properties of an XLS file 
(pre-Office 2007):

        // Open the Excel file
        //
        FileInputStream xlsFileStream = new FileInputStream(listFile[i]);
        HSSFWorkbook wb = new HSSFWorkbook(xlsFileStream);
        ExcelExtractor txex1 = new ExcelExtractor(wb);

        // Extract the custom properties from the workbook
        //
        DocumentSummaryInformation dsi = txex1.getDocSummaryInformation();
        CustomProperties properties = dsi.getCustomProperties();
        if (properties != null)
        {
                Object prop = properties.get("My Property");
                if (prop != null)
                {
                        myProperty = prop.toString();
                }
        }

But now I need to enhance this to read the same properties from an XLSM 
file (Office 2007+)

        // Open the Excel file
        //
        FileInputStream xlsFileStream = new FileInputStream(listFile[i]);
        XSSFWorkbook wb = new XSSFWorkbook(xlsFileStream);
        XSSFExcelExtractor txex1 = new XSSFExcelExtractor(wb);

        // Extract the custom properties from the workbook
        //
        DocumentSummaryInformation dsi = txex1.getDocSummaryInformation();
        CustomProperties properties = dsi.getCustomProperties();
        if (properties != null)
        {
                Object prop = properties.get("My Property");
                if (prop != null)
                {
                        myProperty = prop.toString();
                }
        }

But the XSSLExcelExtractor does not have a method to retrieve the Document 
Summary info.  Am I missing something fundamental about the differences in 
the pre-2007 and post 2007 office files?