code: public byte[] getBytes() {
      ByteArrayOutputStream baos = new ByteArrayOutputStream();
      try {
        workbook.write(baos);
      } catch (IOException e) {
        new RuntimeException(e);
      } finally {
        if (baos != null)
          try {
            baos.close();
          } catch (IOException e) {
            new RuntimeException(e);
          }
      }
      return baos.toByteArray();
    }
docs: Gets the excel file as byte array.
  
  @return byte array which represents the excel file