In the conf/web.xml file look for the following llnes
<!-- The mapping for the JSP servlet -->
<servlet-mapping>
<servlet-name>jsp</servlet-name>
<url-pattern>*.jsp</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>jsp</servlet-name>
<url-pattern>*.jspx</url-pattern>
</servlet-mapping>
These lines map the jsp and jspx extensions to the JSP compiler. You can add or edit these lines to use any extension that you want including html or asp. You can also do this in the web application specific web.xml file to localize the changes to an single application.