code: static Workbook clearContent(final Workbook book) {
          ByteArrayOutputStream originalOut = new ByteArrayOutputStream();
          
          try { book.write(originalOut); }
          catch (IOException e) { throw new CalculationEngineException(e); }
          
          InputStream originalIn = new ByteArrayInputStream(copyOf(originalOut.toByteArray(), originalOut.size()));
  
          Workbook w = ConverterUtils.newWorkbook(originalIn);
          Sheet s = w.getSheetAt(0); //TODO: only one sheet is supported
          
          for (int i = s.getFirstRowNum(); i <= s.getLastRowNum(); i++) {
              Row r = s.getRow(i);
              if (r == null) { continue; }
              
              for (int j = r.getFirstCellNum(); j <= r.getLastCellNum(); j++) {
                  Cell c = r.getCell(j);
                  if (c == null) { continue; }
                  
                  c.setCellType(CELL_TYPE_BLANK);
              }
          }
          
          return w;
      }
docs: Gets an instance of a Workbook ({@link ConverterUtils#newWorkbook(InputStream)}, creates copy of original file,
  clears all the cell values, but preserves formatting.