The best place to go for questions like this is the
Servlet Spec (link in my signature).
SRV.6.2.5 Filters and the RequestDispatcher
New for version 2.4 of the Java Servlet specification is the ability to configure filters
to be invoked under request dispatcher forward() and include() calls.
By using the new <dispatcher> element in the deployment descriptor, the
developer can indicate for a filter-mapping whether he would like the filter to be
applied to requests when:
1. The request comes directly from the client.
This is indicated by a <dispatcher> element with value REQUEST,
or by the absence of any <dispatcher> elements.
2. The request is being processed under a request dispatcher representing the
Web component matching the <url-pattern> or <servlet-name> using a forward()
call.
This is indicated by a <dispatcher> element with value FORWARD.
3. The request is being processed under a request dispatcher representing the
Web component matching the <url-pattern> or <servlet-name> using an include()
call.
This is indicated by a <dispatcher> element with value INCLUDE.
4. The request is being processed with the error page mechanism specified in �Error
Handling� on page 73 to an error resource matching the <url-pattern>.
This is indicated by a <dispatcher> element with the value ERROR.
5. Or any combination of 1, 2, 3, or 4 above.