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tomcat – Java servlet not writing response bytes-Exceptionshub

Posted by: admin February 25, 2020 Leave a comment


I have a few Java servlets (3.x – Tomcat 8) running that generate and return PDF documents. I’ve never had any problems with any of them. I recently wrote a new servlet to also create and return a PDF document, and this new servlet is using the exact same piece of response code as the others are using:

response.setHeader("Content-Transfer-Encoding", "binary");
response.setHeader("Content-Disposition","attachment; filename=\""+filename+".pdf\""); 

System.out.println("# Bytes => " + pdfBytes.length);

ServletOutputStream sos = response.getOutputStream();
BufferedOutputStream bos = new BufferedOutputStream(sos);

As I said, this has been working fine with the others, but when I call the new servlet, it returns 0 bytes, even though the print statement above has a non-zero value.

However, if I change the response writing code above to:

OutputStream os = response.getOutputStream();

…it works fine, returning a well-formed PDF document. Why might this be happening?

How to&Answers:

You’re not flushing the BufferedOutputStream – so it’s buffering all your data. You should flush that, not the ServletOutputStream.

However, if you’re only writing a single byte array, there’s no point in using BufferedOutputStream anyway – and you shouldn’t need to explicitly flush anyway, as closing will flush. So you just need:

ServletOutputStream sos = response.getOutputStream();
// Unclear whether *this* is needed, either.

I’d personally expect the servlet container to close the output stream, but it’s not clear from the docs. Whether you want to close it if an exception occurs is a different matter…


you should really flush and close bos not sos