protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws IOException {
// If an If-Modified-Since header is ever provided, we always say
// not modified. This is because when there actually is a change,
// cache busting should occur.
UrlValidationStatus vstatus = urlGenerator.validateJsUrl(
req.getRequestURL().append('?').append(req.getQueryString()).toString());
if (req.getHeader("If-Modified-Since") != null &&
vstatus == UrlValidationStatus.VALID_VERSIONED) {
resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
return;