Need help in logic

[nn12]

I have a word cloud app which generates a image based upon user input text. This generated image is stored in images folder. I have provided a save image option which allows user to save this image on their desktop. I am doing this by calling a servlet shown below which reads the image stored & writes to byte stream.

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		response.setHeader("Content-disposition","attachment; filename=output.png");
		
		String filename = request.getSession().getServletContext().getRealPath("/")+"/images/output.png";
		String mimeType = "image/png";
		response.setContentType(mimeType);
		
	    File file = new File(filename);
	    response.setContentLength((int)file.length());
	    FileInputStream in = new FileInputStream(file);
	    OutputStream outputStream = response.getOutputStream();

	    byte[] buf = new byte[1024];
	    int count = 0;
	    while ((count = in.read(buf)) >= 0) {
	    	outputStream.write(buf, 0, count);
	    }
	    in.close();
	    outputStream.close();

		
	}

Problem with this approach is, if another user (user 2) meantime generates a word cloud, it replaces output.png with this new image. Now if user 1 tries to save the image, he gets an wrong image(image of user 2).
Can you please suggest me a better approach which will allow to keep images user specific?

[Tolls]

Don't store it in a folder, use a database instead?
Is there a way of identifying a particular user?
Do they log in?
Or is it only via a session id?

[nn12]

yes, i have the user logged in details. But I guess storing every image in the DB would be an overhead. Is it possible to store image in a session & then retrieve it while saving it. If yes, please let me know how.

[Tolls]

Storing in a db (which is essentially disk) is far preferable than trying to hold images in memory.

Provide a single slot in the db to hold an image against the logged in user.

Why are you storing the image anyway? I don't know the flow in your system so I could well be giving bad advice here.