Tomcat´s ExpiresFilter not working on index page

Question

I added the following code to the web.xml of my Tomcat (version 9) server:

<filter>
    <filter-name>CachingFilter</filter-name>
    <filter-class>org.apache.catalina.filters.ExpiresFilter</filter-class>
    <init-param>
        <param-name>ExpiresDefault</param-name>
        <param-value>access plus 14 days</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>CachingFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

It works absolutely fine on any images, scripts, subpages, everything. The response contains an "Expires" header for all resources.

But for the root resource there is no such header and I don´t understand why. There is no error or warning in the logs or anything. Is there maybe a special handling for the root resource so that caching is disabled for that?

EDIT

I activated the logs of the ExpiresFilter to see more details but the logs indicate that the expires header for the root resource is set correctly.

org.apache.catalina.filters.ExpiresFilter.onBeforeWriteResponseBody Request [/] with response status [200] content-type [text/html;charset=UTF-8], set expiration date [10/3/22 4:33 PM]

But the response simply does not contain a Expires-Header or any other caching header.

Answer 1

You can follow the steps that the java doc provided to see exactly what happens.

Troubleshooting