How to add response headers based on Content-type; getting Content-type before the response is committed

Question

I want to set the Expires header for all image/* and text/css. I'm doing this in a Filter. However:

• before calling chain.doFilter(..) the Content-type is not yet "realized"
• after calling chain.doFilter(..) the Content-type is set, but so is content-length, which forbids adding new headers (at least in Tomcat implementation)

I can use the extensions of the requested resource, but since some of the css files are generated by richfaces by taking them from inside jar-files, the name of the file isn't x.css, but is /xx/yy/zz.xcss/DATB/....

So, is there a way to get the Content-type before the response is committed.

Answer 1

Yes, implement HttpServletResponseWrapper and override setContentType().

class AddExpiresHeader extends HttpServletResponseWrapper {
    private static final long ONE_WEEK_IN_MILLIS = 604800000L;

    public AddExpiresHeader(HttpServletResponse response) {
        super(response);
    }

    public void setContentType(String type) {
        if (type.startsWith("text") || type.startsWith("image")) {
            super.setDateHeader("Expires", System.currentTimeMillis() + ONE_WEEK_IN_MILLIS);
        }
        super.setContentType(type);
    }
}

and use it as follows:

chain.doFilter(request, new AddExpiresHeader((HttpServletResponse) response));