Elasticsearch/ES教程（22）：RestClient实现聚合Aggregation

Aggregation 概述

• Aggregation 可以和普通查询结果并存，一个查询结果中也允许包含多个不相关的Aggregation. 如果只关心聚合结果而不关心查询结果的话会把SearchSource的size设置为0，能有效提高性能.

Metrics:

• 简单聚合类型, 对于目标集和中的所有文档计算聚合指标, 一般没有嵌套的sub aggregations. 比如 平均值(avg) , 求和 (sum), 计数 (count), 基数 (cardinality). Cardinality对应distinct count

Bucketing:

• 桶聚合类型, 在一系列的桶而不是所有文档上计算聚合指标,每个桶表示原始结果集合中符合某种条件的子集. 一般有嵌套的sub aggregations. 典型的如TermsAggregation, HistogramAggregation

Matrix:

• 矩阵聚合, 多维度聚合, 即根据两个或者多个聚合维度计算二维甚至多维聚合指标表格. 目前貌似只有一种MatrixStatAggregation. 并且目前不支持脚本(scripting)

Pipeline:

• 管道聚合, 在之前聚合结果的基础上再次进行聚合计算, 往往和Bucketing Aggregation 结合起来使用. 举列: 先求出过去30天每天的交易总金额 (Bucketing aggregation)，再统计交易总金额大于10000的天数 (Pipeline aggregation)

本文讲解在java/springboot中如何使用RestClient聚合

package cn.bdbk.hotel;

import cn.bdbk.hotel.pojo.HotelDoc;
import com.alibaba.fastjson.JSON;
import org.apache.http.HttpHost;
import org.elasticsearch.action.search.SearchRequest;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.search.SearchHit;
import org.elasticsearch.search.SearchHits;
import org.elasticsearch.search.aggregations.AggregationBuilders;
import org.elasticsearch.search.aggregations.Aggregations;
import org.elasticsearch.search.aggregations.bucket.terms.Terms;
import org.elasticsearch.search.fetch.subphase.highlight.HighlightBuilder;
import org.elasticsearch.search.fetch.subphase.highlight.HighlightField;
import org.elasticsearch.search.sort.SortOrder;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;

import java.io.IOException;
import java.util.List;
import java.util.Map;

@SpringBootTest
class HotelSearchTest {

    private RestHighLevelClient client;

    @Test
    void testAggregation() throws IOException {
        SearchRequest request = new SearchRequest("hotel");
        //去掉文档
        request.source().size(0);
        //聚合,三要素 名称 类型 字段
        request.source().aggregation(
                AggregationBuilders.terms("brandAgg")
                        .field("brand")
                        .size(10)
        );
        SearchResponse response = client.search(request, RequestOptions.DEFAULT);

        //解析
        Aggregations aggregations = response.getAggregations();
        //根据名称获取聚合结果
        Terms brandTerms = aggregations.get("brandAgg");

        List<? extends Terms.Bucket> buckets = brandTerms.getBuckets();

        for (Terms.Bucket bucket : buckets){
            String brandName = bucket.getKeyAsString();
            System.out.println(brandName);
        }
    }

    @BeforeEach
    void setUp() {
        client = new RestHighLevelClient(RestClient.builder(
                HttpHost.create("http://170.106.116.159:9200")
        ));
    }

    @AfterEach
    void tearDown() throws IOException {
        client.close();
    }

}