code: public static void checkIfModifiedSince(final String method, final String ifModifiedSince,
              final Instant modified) {
          if (isGetOrHead(method)) {
              final Instant time = parseDate(ifModifiedSince);
              if (time != null && time.isAfter(modified.truncatedTo(SECONDS))) {
                  throw new RedirectionException(notModified().build());
              }
          }
      }
docs: Check for a conditional operation.
  @param method the HTTP method
  @param ifModifiedSince the If-Modified-Since header
  @param modified the resource modification date