code: @Override
    public Map<String, Object> getFileMetaData() {
      if (file == null) {
        file = new HashMap<String, Object>();
      }
      if (file.containsKey(FILE_META)) {
        return (Map<String, Object>) file.get(FILE_META);
      }
      if (localFile != null) {
        Map<String, Object> meta = AVIMFileMessageAccessor.getImageMeta(localFile);
        meta.put(FILE_SIZE, actualFile.getSize());
        file.put(FILE_META, meta);
        return meta;
      } else if (actualFile != null) {
        Map<String, Object> meta = actualFile.getMetaData();
        file.put(FILE_META, meta);
        return meta;
      }
      return null;
    }
docs: 获取文件的metaData
  
  @return