code: public static String[] getXlsxWorksheets(File file) 
          throws IOException
      {
          XlsxWorkbook workbook = XlsxWorkbook.getWorkbook(file);
          String[] sheets = workbook.getSheetNames();
          workbook.close();
          return sheets;
      }
docs: Returns the sheets from the given Excel XLSX file.
  @param file The file with the name of the XLSX file
  @return The sheet names from the XLSX file
  @throws IOException if the file cannot be opened