Returning ZipOutputStream to browser

I have an ZipOutputStream that I want to return to the browser. The experience I would like is that the user clicks an anchor tag, and then a file download prompt is displayed for the ZipOutputStream that I have.

How do you get the ZipOutputStream back to the browser?

Answer

Just had to do this exact same thing yesterday.

    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ZipOutputStream zip = new ZipOutputStream(baos);

    .... populate ZipOutputStream

    String filename = "out.zip";
    // the response variable is just a standard HttpServletResponse
    response.setHeader("Content-Disposition","attachment; filename="" + filename + """);
    response.setContentType("application/zip");

    try{            
        response.getOutputStream().write(baos.toByteArray());
        response.flushBuffer();
    }
    catch (IOException e){
        e.printStackTrace();        
    }
    finally{
        baos.close();
    }

Note I’m using a ByteArrayOutputStream wrapper and toByteArray but you could probably just write any other type of Outputstream directly to the response with a standard InputStream.read() OutputStream.write() loop.

Off hand I’m actually not sure which is faster if any, but I suspect my use of ByteArrayOutputStream here might not be the most memory conscious approach: