Serving static resource with the default servlet works fine...
<servlet-mapping>
<servlet-name>default</servlet-name>
<url-pattern>*.ico</url-pattern>
</servlet-mapping>

...until I add a new default servlet
<servlet-mapping>
<servlet-name>myNewDefaultServlet</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>

In which case *.ico is eventually served by myNewDefaultServlet.

As I was surprised by this behaviour I replaced the "default" by another servlet
<servlet-mapping>
<servlet-name>AnotherServlet</servlet-name>
<url-pattern>*.ico</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>myNewDefaultServlet</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>

This time, the *.ico request is served by AnotherServlet.

The overall behaviour is not consistent. When default servlet is configured to serve a *.ico request, it should serve it always the same way regardless of another servlet defined on / or not