apollo-common/src/main/java/com/ctrip/framework/apollo/common/utils/BeanUtils.java/BeanUtils/toPropertySet
class BeanUtils:  @SuppressWarnings("unchecked")
  public static <K> Set<K> toPropertySet(String key, List<?> list) {
    Set<K> set = new HashSet<>();
    if (CollectionUtils.isEmpty(list)) {// 防止外面传入空list
      return set;
    }
    try {
      Class<?> clazz = list.get(0).getClass();
      Field field = deepFindField(clazz, key);
      if (field == null) {
          throw new IllegalArgumentException("Could not find the key");
      }
      field.setAccessible(true);
      for (Object o : list) {
        set.add((K)field.get(o));
      }
    } catch (Exception e) {
      throw new BeanUtilsException(e);
    }
    return set;
  }