Downloading a file via JSP

Question

I am trying to write some code which will generate a file and then download the file
from my Webserver. When I download the file I get "Error 500: OutputStream already obtained"
appended to the file. I can't work out why this is so.
Here is the code I have used to download the file.
I have also included the file before and after transmission.
Any help would be appreciated.
<%@page import="java.net.*,javax.servlet.http.*,javax.servlet.*,java.io.*" %>
<%
ServletOutputStream out1 = response.getOutputStream();
String fileName = (String)request.getParameter("filename");
// MIME type for pdf doc
response.setContentType("application/x-download");
response.setHeader("Content-Disposition","attachment;filename="+fileName+";");
File f = new File("\\"+fileName);
FileInputStream stream = new FileInputStream(f);
BufferedInputStream bis = new BufferedInputStream(stream);
BufferedOutputStream bos = new BufferedOutputStream(out1);
byte[] buff = new byte[2048];
int bytesRead;
// Simple read/write loop.
try {
while (-1 != (bytesRead = bis.read(buff, 0, buff.length))) {
bos.write(buff, 0, bytesRead);
} catch (Exception e) {
if (bos != null) bos.close();
e.printStackTrace();     
finally {
if (bis != null) bis.close();
if (bos != null) bos.close();     
if (stream != null) stream.close();     
%>
This is the file on the WebServer
The Quick Brown Fox Jumps Over The Lazy Dog
The Quick Brown Fox Jumps Over The Lazy Dog
The Quick Brown Fox Jumps Over The Lazy Dog
This is the file after it has been transferred
The Quick Brown Fox Jumps Over The Lazy Dog
The Quick Brown Fox Jumps Over The Lazy Dog
The Quick Brown Fox Jumps Over The Lazy DogError 500: OutputStream already obtained
Thanks
Adrian Campbell
Honda Australia

Answer 1

The JSP automatically gets an outputstream/writer, and starts writing to the output. In fact thats where the implicit variable "out" comes from.
Couple of things to be aware of:
Every carriage return outside of a <% %> tag in a JSP gets converted directly into the html as out.println("\r\n");
That means the generated servlet has started writing even before you get the outputstream - which is what raises the exception.
There are two ways to stop this
1 - write it in a servlet - its purely code, with no HTML so servlet is better suited.
2 - have no carriage returns outside of JSP tags <% %>. You currently have one - one the very first line. Try it like this:
<%@page import="java.net.*,javax.servlet.http.*,javax.servlet.*,java.io.*" %><% 
ServletOutputStream out1 = response.getOutputStream();
%>  // and no carriage return at the end eitherThat should do it.
As an aside, if you are going to be generating a text file, then you can use the implicit writer "out" as opposed to the OutputStream.
Cheers,
evnafets