Is doFilter() executed before or after the Servlet's work is done?

Question

The javax.servlet.Filter object can be used both for authentication (where the Filter needs to catch the request before any servlet work needs to be done) and for XSLT translation (where the servlet needs to be completely finished generating content). When does it actually get executed?

I know this is implementation dependent (on the web container), but this seems to be problem that needs to be solved by all of them.

Maybe there is a configuration option set somewhere for each Filter registration with the web container?

Additional:

Also, what governs the order of Filter execution? Why would FooFilter get executed before BarFilter?

Answer 1

The filter chain in essence wraps the servlet invocation. The chain will process all links until it hits the "bottom", then allow the servlet to run, and then return up the chain in reverse. For example, if you have a new "example filter", your doFilter() method may look like this:

public void doFilter(ServletRequest request,
      ServletResponse response, FilterChain chain) 
      throws IOException, ServletException {
// do pre-servlet work here
chain.doFilter(request, response);
// do post servlet work here

}

Answer 2

alt text http://img228.imageshack.us/img228/8945/filter.png

About the order: as I remember from spec servlet container doesn't guarantee that filters will be called in some order.

Answer 3

According to the servlet2.3 specification filter is performed according to web.xml configuration of filter- mapping sequence Ref-http://www.programering.com/a/MTMyADOwATI.html