code: public <T> T getDocument(String indexName, String indexType,String documentId,Class<T> beanType) throws ElasticSearchException{
  		return getDocument(  indexName,   indexType,  documentId,(Map<String,Object>)null,beanType);
  	}
docs: 获取文档对象
  @param indexName
  @param indexType
  @param documentId
  @return
  @throws ElasticSearchException