1. in order to really work, your web(app) server should have direct acces to it. As this is not the case when working with the temp dir (at least not without additional configuring), the requests will go through Servlets. And to have maximum gain, you want your server to regconize that the client is requesting a static resource, not a dynamic servlet.
2. the start of the solution would be:
a. to get rid of the constantly changing urls (though this might not be possible as the rendercount is important for our stale page tracking);
b. set an expiration header (e.g. to epoch) for selected resources.
I guess if 2. is solved, we won't be needing one, do we?
Eelco
Jonathan Locke wrote:
yeah, but this isn't a long term solution. we ought to be able to return
images that get cached... even dynamically generated ones. there ought
to be a way to fudge the rendercount stuff so the browser will cache images.
On Tue, 4 Jan 2005, Johan Compagner wrote:
You can write to disk in a webapplication Use the work dir:
ServletContext.getAttribute("javax.servlet.context.tempdir");
That will return a File object that points to the work dir for the current webapplication.
Gili wrote:
Ok, so to rehash some points:
1) Currently we parameterize the image URL on the session ID and parameters used to render the image 2) We write out the image to disk somewhere (although I don't know where, can you elaborate?)
My personal requirements are:
1) Render image once per page, not per session or view. 2) Do not expose image parameters if possible. Ideally the URL should read "image<number>.<extension>" and we'll have some lookup table somewhere that maps image creation parameters to image URLs -> reuse the same image if the same parameters are used (server-side).
I remember reading about JBoss not giving you write access to the webapp dir (heck, you could be running inside a JAR). I feel this problem related to handling links to images in general, not just dynamically generated ones, if their URL falls under the servlet context path.
What we could do (solves all problems I know about) is handle image URLs within the WebApp servlet itself. That is, we never write the images to disk if they're dynamically generated and "cacheDir" (some new property I made up) is not set. For JBoss and others cacheDir will be unset so it'll default to caching in memory. For Tomcat and others, it'll be set to the default temporary directory for the webapp so we'll cache to disk. What will happen is that someone will refer to /MyWebApp/myImage.jpg -- the servlet will recognize that the URL refers to an image, use the appropriate resource location mechanisms -- and stream back the image (whether dynamic or static). And ideally we'd throw in a "image parameters -> image URL" mapping somewhere so we don't have to expose inner details to the HTTP clients.
My only concern is that for JBoss, dynamically generated images would be expensive. Still, I don't think we have a choice in such cases if we absolutely cannot write to any directory. What do you think?
Gili
On Tue, 04 Jan 2005 15:45:50 +0100, Eelco Hillenius wrote:
None yet. We're thinking about it.
Eelco
Gili wrote:
I saw a lot of discussion of the various problems and possible solutions but none of them was agreed upon because they each had their own problem. All I know is that in my case the dynamically-generated images should be treated as cacheable because they will not change with clicks (i.e. reference count). What is the proposed solution?
Gili
On Tue, 04 Jan 2005 13:03:00 +0100, Eelco Hillenius wrote:
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