Warning response header

[Sean Dawson]

Tomcat 8_32
Windows 7
Java 8_51
RestEasy 3.0.11.Final
GWT 2.7.0 (Jetty jetty-9.3.5.v20151012)

Servlet code makes a RestEasy call to another servlet (same container) -
second servlet sets the 'Warning' HTTP header on response.  Would like to
access that in first servlet but when running in Tomcat, that header is not
included.

Code to get header in first servlet:

Object headers = ((ClientResponseFailure)
e).getResponse().getResponseHeaders().get("Warning");

Also tried: getHeaders(), getStringHeaders(), and getHeaderString().

When running GWT in superdev mode in IntelliJ (15.0.4) using Jetty, the
above returns a List with one item that contains the warning string.  When
remote debugging Tomcat, that call returns null.

Added this to web app xml, and also tried Tomcat conf/web.xml...

    <filter>
        <filter-name>CorsFilter</filter-name>
        <filter-class>org.apache.catalina.filters.CorsFilter</filter-class>
        <init-param>
            <param-name>cors.exposed.headers</param-name>
            <param-value>Warning</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>CorsFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

Also tried cors.allowed.headers.

Any pointers?