code: public MessageBroker processAfterStartup(MessageBroker broker) {
          // Eagerly detect possible problems with the Service
          Service service = broker.getServiceByType(getServiceClassName());
          Assert.notNull(service, "The MessageBroker with id '" + broker.getId() + "' does not have a service of type " + getServiceClassName()
              + " configured.");
          Assert.isTrue(service.isStarted(), "The Service with id '" + service.getId() + "' of MessageBroker with id '" + broker.getId()
              + "' was not started as expected.");
          return broker;
      }
docs: Error checking is done on the started MessageBroker to ensure configuration was successful.
  
  @see MessageBrokerConfigProcessor#processAfterStartup(MessageBroker)