code: @Override
    protected boolean beforeExport() {
      if (null == attrs) {
        String keys = context.get("keys", String.class);
        if (Strings.isNotBlank(keys)) {
          attrs = Strings.split(keys, ",");
        }
      }
      if (null == propertyExtractor) {
        propertyExtractor = context.get("extractor", PropertyExtractor.class);
      }
      if (null == attrs || null == propertyExtractor) {
        logger.debug("attrs or propertyExtractor is null,transfer data as array.");
      }
      return super.beforeExport();
    }
docs: {@inheritDoc}