code: public static Class<?> getGenericFieldType(Field field) {
          ParameterizedType stringListType = (ParameterizedType) field.getGenericType();
          Class<?> clazz = (Class<?>) stringListType.getActualTypeArguments()[0];
          return clazz;
  	}
docs: 获得泛型的class
  @param field
  @return