code: public static <T extends Entity<?>> List<?> extractIds(Collection<T> entities) {
      List<Object> idList = CollectUtils.newArrayList();
      for (Iterator<T> iter = entities.iterator(); iter.hasNext();) {
        Entity<?> element = iter.next();
        try {
          idList.add(PropertyUtils.getProperty(element, "id"));
        } catch (Exception e) {
          logger.error("getProperty error", e);
          continue;
        }
      }
      return idList;
    }
docs: <p>
  extractIds.
  </p>
  
  @param entities a {@link java.util.Collection} object.
  @param <T> a T object.
  @return a {@link java.util.List} object.