code: protected HttpHandler getHttpHandler() {
  		// Use bean names so that we don't consider the hierarchy
  		String[] beanNames = getBeanFactory().getBeanNamesForType(HttpHandler.class);
  		if (beanNames.length == 0) {
  			throw new ApplicationContextException(
  					"Unable to start ReactiveWebApplicationContext due to missing HttpHandler bean.");
  		}
  		if (beanNames.length > 1) {
  			throw new ApplicationContextException(
  					"Unable to start ReactiveWebApplicationContext due to multiple HttpHandler beans : "
  							+ StringUtils.arrayToCommaDelimitedString(beanNames));
  		}
  		return getBeanFactory().getBean(beanNames[0], HttpHandler.class);
  	}
docs: Return the {@link HttpHandler} that should be used to process the reactive web
  server. By default this method searches for a suitable bean in the context itself.
  @return a {@link HttpHandler} (never {@code null}