Unable to change content-type with Interceptor?

[Burton Rhodes]

I'm not sure what I'm doing wrong, but I cannot for the life of me change
the content-type of the response using an interceptor.  My interceptor code
is below.  The example below seems a bit absurd, but eventually I will add
code to change the content-type dynamically from "application/json" to
"text/plain" depending on what the request will "accept" (this is to fix an
IE bug related to ajax file uploads).  What am I missing here?  Many thanks
in advance.

<!-- struts.xml snippit -->
<package name="jsonSecure" namespace="/app/json" extends="json-default">

    <interceptors>
        <interceptor name="jsonDynamicContentType"
class="com.afs.web.interceptor.JsonDynamicContentTypeInterceptor"/>
        <interceptor-stack name="dynamicContentType">
            <interceptor-ref name="json"/>
            <interceptor-ref name="jsonDynamicContentType"/>
        </interceptor-stack>
    </interceptors>

    <action name="TeamFileJson_upload"
class="com.afs.web.action.json.TeamFileJsonAction" method="upload">
        <interceptor-ref name="dynamicContentType"/>
        <result type="json"/>
    </action>


<!-- Custom Interceptor -->
public class JsonDynamicContentTypeInterceptor  extends AbstractInterceptor
{

    public String intercept(ActionInvocation invocation) throws Exception {

        // Go down the chain first
        String result = invocation.invoke();

        // Change the content-type of the response
        HttpServletRequest request = ServletActionContext.getRequest();
        HttpServletResponse response = (HttpServletResponse)
invocation.getInvocationContext().get(StrutsStatics.HTTP_RESPONSE);
        response.setContentType("text/plain");

        // This doesn't work either
        response.setHeader("Content-Type","text/plain");

        // Continue the chain
        return result;

    }

}