黑马聚合的分类及实现

1、什么是聚合?

聚合是对文档数据的统计、分析、计算

聚合的常见种类有哪些?
桶(Bucket)聚合:用来对文档做分组
TermAggregation:按照文档字段值分组

Date Histogram:按照日期阶梯分组，例如一周为一组，或者一月为一组

        度量(Metric)聚合:用以计算一些值，比如:最大值、最小值、平均值等
                AVg:求平均值
                Max:求最大值
                Min:求最小值
                Stats:同时求max、min、avg、sum等

Pipeline:基于其它聚合结果再做聚合

参与聚合的字段类型必须是:
        keyword
        数值
        日期
        布尔

2、DSL实现Bucket聚合

可以新增在aggs内order字段以自定义排序规则，也可以在最外层新增query来限定聚合范围

aggs代表聚合，与query同级，此时query的作用是?

限定聚合的的文档范围

聚合必须的三要素:
        聚合名称
        聚合类型
        聚合字段

聚合可配置属性有:
        size:指定聚合结果数量
        order:指定聚合结果排序方式
        field:指定聚合字段

3、DSL实现Metrics聚合

在聚合类型同级多加一层聚合即可，如图

4、RestClient实现聚合

@Testvoid testAggregation() throws IOException {//1、准备RequestSearchRequest request = new SearchRequest("hotel");//2、准备dslrequest.source().size(0);request.source().aggregation(AggregationBuilders.terms("brandAgg").field("brand").size(10));//3、发出请求SearchResponse response = client.search(request, RequestOptions.DEFAULT);//4、解析结果Aggregations aggregations = response.getAggregations();Terms brandTerms = aggregations.get("brandAgg");List<? extends Terms.Bucket> buckets = brandTerms.getBuckets();for (Terms.Bucket bucket : buckets) {String keyAsString = bucket.getKeyAsString();System.out.println(keyAsString);}}

封装请求信息逐层封装，解析相应结果逐层解析即可

注意返回值类型与方法传参，ctrl+p可以提示方法所需形参类型

多条件聚合只需增加aggregations，并在取出结果时逐一拆分即可

    @Overridepublic Map<String, List<String>> filters() {try {SearchRequest request = new SearchRequest("hotel");Map<String, List<String>> result = new HashMap<>();buildAggregation(request);SearchResponse response = client.search(request, RequestOptions.DEFAULT);Aggregations aggregations = response.getAggregations();List<String> brandlist = getAggByName(aggregations,"brandAgg");result.put("品牌",brandlist);result.put("星级",getAggByName(aggregations,"starNameAgg"));result.put("城市",getAggByName(aggregations,"cityAgg"));return result;} catch (IOException e) {throw new RuntimeException(e);}}private static List<String> getAggByName(Aggregations aggregations,String aggName) {Terms brandterms = aggregations.get(aggName);List<String> brandlist = new ArrayList<>();List<? extends Terms.Bucket> buckets = brandterms.getBuckets();for (Terms.Bucket bucket : buckets) {brandlist.add(bucket.getKeyAsString());}return brandlist;}private static void buildAggregation(SearchRequest request) {request.source().aggregation(AggregationBuilders.terms("brandAgg").size(100).field("brand"));request.source().aggregation(AggregationBuilders.terms("cityAgg").size(100).field("city"));request.source().aggregation(AggregationBuilders.terms("starNameAgg").size(100).field("starName"));}