Upgrading from .xls to .xlsx with POI

I have a web application In which i have excel file(.xls) download option. Now I Have to provide that feature in .xlsx

I am trying to Use POI Jar. When I try to do that as a stand alone Application it works fine, but when I try to integrate that into a web application, I am getting an error as

Excel Found Unreadable Content in FILENAME.xlsx. do you want to recover the content of this workbook?
If you trust the source of this workbook click yes!

XSSFWorkbook w = FileName.createExcelWorkbookPosition(
        request.getParameter("BSNS_DT"));
response.setContentType(
        "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
response.setHeader("Content-Disposition","attachment;filename=filename.xlsx");
w.write(response.getOutputStream());

Here's the Java code where I create the spreadsheet:

public static XSSFWorkbook createExcelWorkbookPosition(String BsnsDate)
    throws Exception
{
    FileOutputStream out = new FileOutputStream("workbook.xlsx");

    // create a new workbook
    XSSFWorkbook wb = new XSSFWorkbook();
    // create a new sheet
    XSSFSheet s = wb.createSheet();
    // declare a row object reference
    XSSFRow r = null;
    // declare a cell object reference
    XSSFCell c = null;

    // header row and columns
    r = s.createRow(0);
    c = r.createCell(0);
    c.setCellValue("Business Date");    
    //c.setCellStyle(cs);
    c = r.createCell(1);
    c.setCellValue("Account No");

    try {
        wb.write(out);
        out.close();
        System.out.println("File writed");
    } catch (Exception e) {
        System.out.println("Error");
        System.out.println(e);
    }
    return wb;
}

Can anyone please help? Sorry for any bad English! Thanks.

I had a quite similar issue, please have a look at Forcing the browser to download a docx file in JAVA generates a corrupted document. The point was to add the Content-Length header of the response.

Try to make createExcelWorkbookPosition returning the file instead of the XSSFWorkbook:

public static File createExcelWorkbookPosition(String BsnsDate) throws Exception {  
    File file = new File("workbook.xlsx");
    FileOutputStream out = new FileOutputStream(file);
    // ...  
    return file;
}

Then:

File file = FileName.createExcelWorkbookPosition(request.getParameter("BSNS_DT"));
// ...
response.setContentLength((int) file.length());    

InputStream in = new FileInputStream(file);
OutputStream out = response.getOutputStream();
byte[] buffer = new byte[1024];
int len;
while ((len = in.read(buffer)) != -1) {
    out.write(buffer, 0, len);
}
// if using Apache IO, the above code can be simplified to IOUtils.copy(in, out);
// if using Guava, Files.copy(file, out);

// don't forget to close your streams and flush the response buffer