code: public void addResourceBase(String resourceBaseDir) {
          // handles resources like images, files, etc..
          logger.info("HttpServer [{}] adding resource base dir [{}]", configuration.safeGetName(), resourceBaseDir);
          ResourceHandler resourceHandler = new ResourceHandler();
          resourceHandler.setResourceBase(resourceBaseDir);
          handlers.addHandler(resourceHandler);
      }
docs: Adds a directory for resources such as files containing html, images, etc.
  to be served up automatically be this server.<br>
  CAUTION: A resource base can only be added BEFORE the server is started.
  @param resourceBaseDir The directory containing resources (basically the
  web root)