Java Filters Performance Question

Question

I have two questions. The first is do Filters add a lot of overhead to request. We have a filter and it is set to run on the URL pattern /*. This means it also runs on all the image request. I think that this is not good for performance, but my co-workers think that it doesn't matter if the filter runs 5 or 6 times per request because the filter only has a couple of if statements.

Is there a way to have the filter run once per request, ignoring the image request.

Thanks Doug

Answer 1

Measuring is knowing. If well-written, I'd say, it's negligible. But if it's for example grabbing the session regardless of it's been created (and thus there's a chance that it will unnecessarily be created), then it may have a noticeable impact on performance and/or memory usage because creation of sessions isn't per-se cheap and sessions are stored in sever's memory for a longer term than the requests.

You may want to replace the url-pattern of /* by *.jsp or to move the restricted pages to a specific folder, e.g. /secured, /private, /pages, etc and alter the url-pattern accordingly to /secured/*, /private/*, /pages/*, etc and put all the static content in a different place, e.g. /static. This way the filter won't be invoked for static content anymore.

Answer 2

First, I agree with the Profile-first approach.

Second, as far as I know it depends, web-server use the same technique to invoke a specific servelt(/JSP) as they use for filters.

In case the filter is filtering a static resource(e.g. jpg file), it's a bit of a waste, In case the filter is filtering a dynamic resource (e.g. Servlet) it's negligible.. (Most of the Java web frameworks like struts and Jboss-seam are using filters heavily..)