code: private boolean useNotModifiedHeader(HttpServletRequest request, String scriptEtag) {
  		long modifiedHeader = -1;
  		try {
  			modifiedHeader = request.getDateHeader(HEADER_IF_MODIFIED);
  			if (modifiedHeader != -1)
  				modifiedHeader -= modifiedHeader % 1000;
  		} catch (RuntimeException ex) {
  		}
  		String eTag = request.getHeader(HEADER_IF_NONE);
  		if (modifiedHeader == -1) {
  			return scriptEtag.equals(eTag);
  		} else if (null == eTag) {
  			return modifiedHeader <= START_TIME;
  		} else {
  			return scriptEtag.equals(eTag) && modifiedHeader <= START_TIME;
  		}
  	}
docs: Determines whether a response should get a 304 response and empty body,
  according to etags and if-modified-since headers.
  
  @param request
  @param scriptEtag
  @return