This would work, but it will not include the time for the response to travel up the filter chain again. So if you do any post processing in any filters (code that runs after chain.doFilter() ), the time that it uses will not be included.

Many filters use post-actions oscache is one of them, take a look at http://kickjava.com/src/com/opensymphony/oscache/web/filter/CacheFilter.java.htm

To solve this, you are forced to use a wrapper and record the total time, i.e:
Time from you hit the first filter, goes down the chain to the Servlet/JSP, and then moves back up the filter chain.

@Thomas Eggum: Great observation, this code will not work. I had actually fixed the code, but forgot to post an update. Your approach works too (creating a StringWrapper). I chose a much simpler approach. Just before chain.doFilter(), store the “START_TIME” in the request.

request.setAttribute("START_TIME",
startTime);
filter.doChain();


In the JSP:

< %
Date startTime = (Date) request.getAttribute("START_TIME");
Date endTime = new Date();
pageTracker._trackEvent("Response time",
"",
"< %=uri%>",
"< %= (endTime - startTime) %>");
%>


The only downside of this approach is that it calculates the time it took from the beginning of the page to that line, so you have to place the line at the bottom of your page.

As far as I can see this example will not work, because the code in your footer will run before the code after chain.doFilter(request, response) in the filter, thus the request-attribute “RESPONSE_TIME” will not be available.

I would suggest to use a StringWrapper to pass down the filter chain to enable inserting of the JavaScript with “pageTracker._trackEvent” when the chain.doFilter(request, response) returns in the filter.

While it’s true that your method is great to chart website performance, you should be aware that an event automatically triggered on every page counts as a gif request to Google analytics, and will therefore always generate a bounce rate of 0%, which is not ideal in a production environment.

Hope this helps.