How do I tell tomcat to support CORS for static content?

Starting with Tomcat 7.0.41, you can easily control CORS behavior via a built-in filter.

References:

• Tomcat 7
• Tomcat 9

Pretty much the only thing you have to do is edit the global web.xml in CATALINA_HOME/conf and add the filter definition:

     <!-- ================== Built In Filter Definitions ===================== -->

      ...

     <filter>
       <filter-name>CorsFilter</filter-name>
       <filter-class>org.apache.catalina.filters.CorsFilter</filter-class>
     </filter>
     <filter-mapping>
       <filter-name>CorsFilter</filter-name>
       <url-pattern>/*</url-pattern>
     </filter-mapping>

    <!-- ==================== Built In Filter Mappings ====================== -->

Be aware, though, that Firefox does not like Access-Control-Allow-Origin: * and requests with credentials (cookies): when responding to a credentialed request, server must specify a domain, and cannot use wild carding.

If you want to debugs requests in this situation, please be aware that CORS headers are only sent if there is a cross-origin request according to this flow-chart:

(tomcat.apache.org/tomcat-8.0-doc/images/cors-flowchart.png)