docs: private static ServiceProviderFinder _getServiceProviderFinderFromInitParam(ExternalContext context)
      {
          String initializerClassName = context.getInitParameter(SERVICE_PROVIDER_FINDER_PARAM);
          if (initializerClassName != null)
          {
              try
              {
                  // get Class object
                  Class<?> clazz = ClassUtils.classForName(initializerClassName);
                  if (!ServiceProviderFinder.class.isAssignableFrom(clazz))
                  {
                      throw new FacesException("Class " + clazz 
                              + " does not implement ServiceProviderFinder");
                  }
                  
                  // create instance and return it
                  return (ServiceProviderFinder) ClassUtils.newInstance(clazz);
              }
              catch (ClassNotFoundException cnfe)
              {
                  throw new FacesException("Could not find class of specified ServiceProviderFinder", cnfe);
              }
          }
          return null;
      }