ES客户端RestHighLevelClient的使用

RestHighLevelClient 是 Elasticsearch 的一个高级客户端，它提供了基于Elasticsearch的REST API的高级API。以下是一个使用 RestHighLevelClient 的示例，它创建了一个索引，添加了一些文档，并执行了一个简单的搜索。

import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.client.indices.CreateIndexRequest;
import org.elasticsearch.client.indices.GetIndexRequest;
import org.elasticsearch.action.index.IndexRequest;
import org.elasticsearch.action.search.SearchRequest;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.action.support.WriteRequest;
import org.elasticsearch.common.xcontent.XContentType;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.search.builder.SearchSourceBuilder;
 
public class ElasticsearchExample {
    public static void main(String[] args) throws IOException {
        // 创建RestHighLevelClient客户端
        try (RestHighLevelClient client = new RestHighLevelClient(
                RestClient.builder(new HttpHost("localhost", 9200, "http")))) {
 
            // 创建索引
            CreateIndexRequest request = new CreateIndexRequest("my_index");
            client.indices().create(request, RequestOptions.DEFAULT);
 
            // 添加文档
            IndexRequest indexRequest = new IndexRequest("my_index");
            indexRequest.id("1");
            indexRequest.source(XContentType.JSON, "title", "Some title");
            client.index(indexRequest, RequestOptions.DEFAULT);
 
            // 确保文档被索引
            client.flush(new FlushRequest("my_index"), RequestOptions.DEFAULT);
 
            // 搜索请求
            SearchRequest searchRequest = new SearchRequest("my_index");
            searchRequest.source(new SearchSourceBuilder().query(QueryBuilders.matchQuery("title", "title")));
 
            // 执行搜索
            SearchResponse searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);
            System.out.println(searchResponse.toString());
        }
    }
}

在这个例子中，我们首先创建了一个 RestHighLevelClient 实例，然后创建了一个名为 "my\_index" 的索引。接着，我们向该索引添加了一个文档，并使用 flush 方法确保文档被立即索引。最后，我们执行了一个基本的搜索，搜索索引中所有标题包