Time the response of our web application (filter does not do the work!)

Question

Hi All,
Hope I can find some help.
Currently I am facing an issue for which I find hard to find a solution.
We are trying to log the time it takes for our web application (in Tomcat) to deliver a page back to the browser.
I decided to use a Filter after having a look on the net, however I believe this approach to be wrong.
I debugged and the doFilter() method is called twice, because the request and the response go through it.
So how can I possibly set the startTime the first time and the stopTime the second time to measure the whole duration?
It is worth mentioning that setting an attribute at the end of the method does not to work.
It seems that when doFilter is called the second time, the req is the object passed in doFilter first time, that is to say, before we set the attribute.
Any idea how to log the real time for the response. Many thanks in advance
public final class TimerFilter implements Filter {
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
        throws IOException, ServletException
     HttpServletRequest httpReq = (HttpServletRequest) req;
     if(httpReq.getAttribute("ALREADY_FILTERED_ONCE") == null){
             this.startTime = System.currentTimeMillis();
     chain.doFilter(request, response);
     if(httpReq.getAttribute("ALREADY_FILTERED_ONCE") != null){
             this.stopTime = System.currentTimeMillis();
          System.out.println("Time to execute request: "  +(stopTime - startTime)+ 
            " milliseconds");
     httReq.setAttribute("ALREADY_FILTERED_ONCE", "");
    }

Answer 1

I don't know, but your description seems to be based on some assumptions in stead of facts.
I debugged and the doFilter() method is called twice, because the request and the response go through it.That seems highly unlikely to me. I can believe that the filter is executed twice, but not because it is for a separate request and response. I would say the filter is executed twice for other reasons.
It seems that when doFilter is called the second time, the req is the object passed in doFilter first time, that is to say, before we set the attribute.And that proves my previous statement, as this would indicate that a whole new request object is created for when the response would be passed through the filter, which is nonsense. I would be more inclined to think that two different requests are happening here, for whatever reason. Are you sure nowhere a redirect is happening?