code: @Override
      protected ModelService getModelService(String serviceName){
          ModelService service = getCache().get(serviceName);
          if (service == null) {
              getCache().putIfAbsent(serviceName,super.getModelService(serviceName));
              service = getCache().get(serviceName);
          }
          return service;
      }
docs: Get the ModelService.
  
  It will query the cache first. If not found in the cache, the service will be added to the cache.
  
  
  @param serviceName
  the Service name.
  @return
  the ModelService.