apache POI - get size of generated excel file

Question

I'm using Apache POI for generating excel file in my spring mvc application. here is my spring action:

 @RequestMapping(value = "/excel", method = RequestMethod.POST)
public void companyExcelExport(@RequestParam String filter, @RequestParam String colNames, HttpServletResponse response) throws IOException{
    XSSFWorkbook workbook = new XSSFWorkbook();
    //code for generate excel file
    //....

    response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
    response.setHeader("Content-Disposition", "attachment; filename=test.xlsx");
    workbook.write(response.getOutputStream());

    response.setHeader("Content-Length", "" + /* How can i access workbook size here*/);
}

I used XSSFWorkbook because i need to generate Excel 2007 format. but my problem is XSSFWorkbook does not have getBytes or getSize method. How can i calculate size of generated xlsx file?

EDIT: I used ByteArrayOutputStream like here:

ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
workbook.write(response.getOutputStream()); 
workbook.write(byteArrayOutputStream);
response.setHeader("Content-Length", "" + byteArrayOutputStream.size());

Answer 1

As @JB Nizet said : set the Header before writing the response .

so what you should do is the following :

ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
workbook.write(byteArrayOutputStream);
response.setHeader("Content-Length", "" + byteArrayOutputStream.size());
workbook.write(response.getOutputStream()); 

and please refer to this answer here , as it describes how to use the ByteArrayOutputStream with the HSSFWorkbook .

Hope that helps .