apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/service/NamespaceService.java/NamespaceService/parseDeletedItems
class NamespaceService:  private List<ItemBO> parseDeletedItems(List<ItemDTO> newItems, Map<String, String> releaseItems, Map<String, ItemDTO> deletedItemDTOs) {
    Map<String, ItemDTO> newItemMap = BeanUtils.mapByKey("key", newItems);

    List<ItemBO> deletedItems = new LinkedList<>();
    for (Map.Entry<String, String> entry : releaseItems.entrySet()) {
      String key = entry.getKey();
      if (newItemMap.get(key) == null) {
        ItemBO deletedItem = new ItemBO();

        deletedItem.setDeleted(true);
        ItemDTO deletedItemDto = deletedItemDTOs.computeIfAbsent(key, k -> new ItemDTO());
        deletedItemDto.setKey(key);
        String oldValue = entry.getValue();
        deletedItem.setItem(deletedItemDto);

        deletedItemDto.setValue(oldValue);
        deletedItem.setModified(true);
        deletedItem.setOldValue(oldValue);
        deletedItem.setNewValue("");
        deletedItems.add(deletedItem);
      }
    }
    return deletedItems;
  }