code: public MapSearchHit getDocumentHit(String indexName,  String documentId) throws ElasticSearchException{
  		return getDocumentHit(indexName,  _doc,documentId);
  	}
docs: 获取文档MapSearchHit对象，封装了索引文档的所有属性数据
  @param indexName
  @param documentId
  @return
  @throws ElasticSearchException