某学生正在学习ElasticSearch,请你帮他分析下，下列代码的作用是什么? String jsonString = "{" + "\"name\":"Elasticsearch Reference\"," + "\"author\":\"Alex Yang \"," + "\"pubinfo\":\"Beijing,Chinna \","+"\"pubtime\":\"2016-07-16\"," + "\"desc\":\"Elasticsearch is a highly scalable open-source full-text search and analytics engine. \"" + "}"; Map<String,String> params =Collections.singletonMap("pretty","true"); HttpEntity ent=new NStringEntity(jsonString,ContentType,APPLICATION_JSON); Response response = restClient.performRequest("PUT","/" + index + "/" + type + "/" +id, params, entity);