In order to do this you may also need to set the filter to run on FORWARD (and INCLUDE as your code shows, although you state you want a FORWARD):
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
<dispatcher>REQUEST</dispatcher>
<dispatcher>FORWARD</dispatcher>
<dispatcher>INCLUDE</dispatcher> <!-- If you want includes as well -->
</filter-mapping>