Generating images on the fly to use as backgrounds for components

Question

I am creating an application that has an input number slider with a background image. I would like to change the background image on the slider based on its position (as chosen by the user) using a partial trigger.
I have successfully been able to do update the background images if I have these images inside of my "Web Content" folder within my JDeveloper project. Instead, I would like to be able to generate the images as needed. These images are color gradients where the start/stop of the gradient is based on the slider's thumb position (as well as other user-defined variables). Because there are many different images that could possibly be created, I am looking into generating the images at runtime rather than have hundreds of images stored somewhere.
I am trying to generate these images using a BufferedImage that I can then write to a file. The path I am saving it at is as follows:
FacesContext fc = FacesContext.getCurrentInstance();
ServletContext sc = (ServletContext)fc.getExternalContext().getContext();
String path = sc.getRealPath("/") + filename;
I then create the file at the path and use ImageIO to write it:
File f = new File(path);
ImageIO.write(bi, "png", f);
I am saving this file path in a variable in my backing bean that I then use on my ADF page to populate the background image field of the slider.
Problem: when I run the page, my slider does not have a background image.
Looking at the location where the file should be saved, it is actually "saving" it within a .war file which I don't think is appropriate (or possible, for that matter). Is there some way that I can save it either on the server side or the client side so that the client can see the background actually being updated using the generated image? I am almost positive that the path I listed above is incorrect - if this is the correct approach for this problem, where would be an appropriate location?
Any pointers would be greatly appreciated. Thanks in advance for your help!

Answer 1

Instead of saving the image to a file, why not use a Servlet to write the image to the Servlet's response stream. Then, you just point the background image to the Servlet.
John