Replace Image with out user noticing - image

Question

I'm using JSF 2.1.7 + Prime Faces + Prime Faces Mobile.
I have a page that references a image:
<img src="/charts/chart1.png"/>
There's a separate background process that runs to update chart1.png every 2 minutes. (It gets the image from a particular online url). Here is the code I use to save the image:
public static String saveImage(final String strurl, final String imageFileName){
//assume the url for the image is valid
try {
URL url = new URL(strurl);
HttpURLConnection conn = (HttpURLConnection )url.openConnection();
conn.setConnectTimeout(1000); //1 sec timeout
conn.connect();
File file = new File(imageFileName);
BufferedImage image = ImageIO.read(conn.getInputStream());
ImageIO.write(image, "png", file);
return file.getAbsolutePath();
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
ImageIO.write will delete the existing image file and write out a new one. I believe the above will result in a few milliseconds where the image file is not available, and hence the web user will not be able to see the image.
My questions are:
1) Is it true that there will be a time where the image is temporarily unavailable?
2) And if that is the case, what is a possible solution to fix this, so that user will always have a available image?
Thanks in advance. =)

Answer 1

Heres what i would do
1) First instead of replacing the image, i create a new image chart2.png
2)Then I would change the url in the IMG tag to point to a Servlet,
say
and in that servlet which will be mapped to /charts/showchart
,
And in the servlet i would check for latest available PNG , and stream it as response.
This way you customize how or what image you show.