code: private static FilterInitializer[] getFilterInitializers(Configuration conf) {
      if (conf == null) {
        return null;
      }
  
      Class<?>[] classes = conf.getClasses(FILTER_INITIALIZER_PROPERTY);
      if (classes == null) {
        return null;
      }
  
      FilterInitializer[] initializers = new FilterInitializer[classes.length];
      for(int i = 0; i < classes.length; i++) {
        initializers[i] = (FilterInitializer)ReflectionUtils.newInstance(
            classes[i], conf);
      }
      return initializers;
    }
docs: Get an array of FilterConfiguration specified in the conf