In Tomcat

Add the following in your $TOMCAT_HOME/conf/web.xml:

<servlet-mapping>
  <servlet-name>jsp</servlet-name>
  <url-pattern>*.jsp</url-pattern>
  <url-pattern>*.html</url-pattern>
</servlet-mapping>

In Resin

Add the following in $RESIN_HOME/conf/app-default.xml:

<servlet-mapping url-pattern="*.html" servlet-name="resin-jsp"/>