In Struts2 HOWTO set cache headers for static content NOT placed in the standard /struts/, /template/ directories

Question

I have a Struts2 (version 2.2.6) web application where I want to set the Expires response header for static resources that are not present in the traditional static-related folders for struts2. E.g. they are placed under /images/, /css/, /js/ at the root. I want all the resources to have a custom Expires response header.

How to do this in Struts2?

Answer 1

So based on the hint provided by @Dave I have come up with a following approach.

In web.xml setup following filter & it's mapping.

<filter>
    <filter-name>StaticContentCacheHeaderFilter</filter-name>
    <filter-class>management.filters.StaticContentCacheHeaderFilter</filter-class>
</filter>

<filter-mapping>
    <filter-name>StaticContentCacheHeaderFilter</filter-name>
    <url-pattern>/images/*</url-pattern>
</filter-mapping>

And the StaticContentCacheHeader which implements Filter has the following method -

@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

    HttpServletResponse response = (HttpServletResponse) servletResponse;
    HttpServletRequest request = (HttpServletRequest) servletRequest;

    long ifModifiedSince = 0;
    try {
        ifModifiedSince = request.getDateHeader("If-Modified-Since");
    } catch (Exception e) {
        LOG.warning("Invalid If-Modified-Since header value: '"
                + request.getHeader("If-Modified-Since") + "', ignoring");
    }

    long now = DateTime.now().getMillis();

    long lastModifiedMillis = now;

    DateTime dateTime = new DateTime();

    //1 month seems to be the minimum recommended period for static resources acc to          
    //https://developers.google.com/speed/docs/best-practices/caching#LeverageBrowserCaching
    long expires = dateTime.plusMonths(1).getMillis();

    if (ifModifiedSince > 0 && ifModifiedSince <= lastModifiedMillis) {
        // not modified, content is not sent - only basic
        // headers and status SC_NOT_MODIFIED
        response.setDateHeader("Expires", expires);
        response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
        return;
    }

    // set heading information for caching static content
    response.setDateHeader("Date", now);
    response.setDateHeader("Expires", expires);
    response.setDateHeader("Retry-After", expires);
    response.setHeader("Cache-Control", "public");
    response.setDateHeader("Last-Modified", lastModifiedMillis);

    filterChain.doFilter(servletRequest, servletResponse);
}

This will set the cache headers to expire in one month from now.

Let me know if there is a better way to deal with this.