Entry
How do I prevent Netscape 6 from caching generated images? The header settings described in the PHP manual does not seem to work for images.
Jul 18th, 2001 23:40
Martin Seebach, David Bray,
Not sure what you mean by generated images but here is an answer for
you anyway.
For some reason netscape ignores cache headers and expires headers that
are attached to an image generated by a servlet. As a result netscape
will not go back to the server, for images where the URL is a servlet,
unless the user presses refresh.
However you can spoof netscape into thinking the image is at a
different URL each time. In order to do this you are going to need to
use javascript or java in a JSP and generate two random integers.
Attach these random integers to the end of the servlet url as a
name/value pair as follows
servletURL?randomInt1=randomInt2
When you reload the page the integers will be two new numbers, netscape
will think that the URL is different to the URL's of the images it has
cached and will happily go off to the server and request the new image.
Remember this is a workaround for some unlikeable functionality in
Netscape Six (I wisk the Punisher would kill all of Netscape it brings
the web down a notch, and put all of the money into opera) it is not
necessarily an efficient solution.
David Bray
-----
By generated images I meant those by you described as generated by a
servlet.
However, your way to add to the filename is not the simplest one. I use
something like img.php?t=time() where time() returns the internal time
of the server. You are sure to get a unique number with each request
unlike your way where you (theoretically!) could end up getting the
same combination twice.
Another method I found useful, is that if the dynamic part of your
image is dependant on a file, you can add the modified time of that
file to the image name
<img src="img.php?t=<?php echo filemtime($filename) ?>">
and thus only forcing the browser to recache the image if it actually
changes.
Martin Seebach
