code: public static boolean handleIfUnmodifiedSince(final HttpServerExchange exchange, final Date lastModified) {
          return handleIfUnmodifiedSince(exchange.getRequestHeaders().getFirst(Headers.IF_UNMODIFIED_SINCE), lastModified);
      }
docs: Handles the if-unmodified-since header. returns true if the request should proceed, false otherwise
  
  @param exchange     the exchange
  @param lastModified The last modified date
  @return