奇怪的servlet响应问题

Question

I have a servlet witch is generating a .xls file and then it's sending the generated file to the user for download with the code below:

// Write the output to a file
Calendar currentDate = Calendar.getInstance();
SimpleDateFormat formatter= 
new SimpleDateFormat("yyyy_MMM_dd");
String dateNow = formatter.format(currentDate.getTime());

String path = "webapps/myapp/exports/";
String fileName = ("Table_export_"+ dateNow + ".xls");

FileOutputStream fileOut = new FileOutputStream(path+fileName);
wb.write(fileOut);
fileOut.close();
response.setContentType("application/vnd.ms-excel");
response.setHeader("Content-Disposition","attachment;filename="+fileName);

The file is saved on the server with a size of 5 kb, but after the browser dialog and after choosing save or open, the file is empty and the size is 0 kb. I can not understand what is wrong.

I'm fighting with this issue for about 2 hours without a success. I have tried to set the full path:

response.setHeader("Content-Disposition","attachment;filename="path+fileName);

But I got a document with a strange name and it also was 0 kb.

I'm pretty sure that I'm missing something really small, but as a junior developer I still can not figure it out.

Answer 1

Since you already have a method that can write your file to an output stream you can simply change your code this way to send it to the user :

Calendar currentDate = Calendar.getInstance();
SimpleDateFormat formatter = new SimpleDateFormat("yyyy_MMM_dd");
String dateNow = formatter.format(currentDate.getTime());

String fileName = ("Table_export_"+ dateNow + ".xls");

response.setContentType("application/vnd.ms-excel");
response.setHeader("Content-Disposition","attachment;filename="+fileName);

OutputStream outputStream = response.getOutputStream();
try {
    wb.write(outputStream);
} finally {
    outputStream.close();
}

It won't be saved on your server HDD though.

The method HttpServletResponse#getOutputStream() allows you to access the stream of bytes that will be sent back to the client.

Answer 2

When you used the format -

String path = "webapps/myapp/exports/";
String fileName = ("Table_export_"+ dateNow + ".xls");
...
response.setHeader("Content-Disposition","attachment;filename="path+fileName);

Was the filename "webapps%2Fmyapps%2Fexports%2fTable_export_....xls"?

Als the filesize would have been zero because you are not putting any data in the file