面试题：ElasticSearch中如何通过顶部命中聚合实现高亮数据提取

实现步骤：
- 构建查询：首先构建一个针对文章内容的查询，例如使用match查询来匹配关键词。
- 设置高亮：为查询结果设置高亮显示，指定需要高亮的字段为文章内容字段。
- 顶部命中聚合：使用顶部命中聚合（top_hits），并设置size为5，以获取每篇文章前5条匹配结果。
关键代码片段（以Python的Elasticsearch客户端为例）：

from elasticsearch import Elasticsearch

es = Elasticsearch()

query = {
    "query": {
        "match": {
            "article_content": "关键词" # 将"关键词"替换为实际要匹配的词
        }
    },
    "highlight": {
        "fields": {
            "article_content": {}
        }
    },
    "aggs": {
        "article_top_hits": {
            "top_hits": {
                "size": 5
            }
        }
    }
}

response = es.search(index="your_index_name", body=query)

在上述代码中：

match查询指定了要匹配的字段article_content和关键词。
highlight部分设置了对article_content字段进行高亮。
aggs中的top_hits聚合确保每篇文章获取前5条匹配结果。your_index_name需替换为实际的索引名称。

如果使用其他语言客户端，原理类似，只是语法会有所不同。例如在Java中使用Elasticsearch Java High - Level REST Client：

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.aggregations.AggregationBuilders;
import org.elasticsearch.search.aggregations.bucket.topn.TopHitsAggregationBuilder;
import org.elasticsearch.search.builder.SearchSourceBuilder;
import org.elasticsearch.search.fetch.subphase.highlight.HighlightBuilder;
import org.elasticsearch.search.fetch.subphase.highlight.HighlightField;

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

public class ElasticsearchExample {
    public static void main(String[] args) throws IOException {
        RestHighLevelClient client = new RestHighLevelClient(
                RestClient.builder(
                        new HttpHost("localhost", 9200, "http")));

        SearchRequest searchRequest = new SearchRequest("your_index_name");
        SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();

        searchSourceBuilder.query(QueryBuilders.matchQuery("article_content", "关键词"));

        HighlightBuilder highlightBuilder = new HighlightBuilder();
        highlightBuilder.field("article_content");
        searchSourceBuilder.highlighter(highlightBuilder);

        TopHitsAggregationBuilder topHitsAggregationBuilder = AggregationBuilders.topHits("article_top_hits").size(5);
        searchSourceBuilder.aggregation(topHitsAggregationBuilder);

        searchRequest.source(searchSourceBuilder);

        SearchResponse searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);

        // 处理结果
        for (SearchHit hit : searchResponse.getHits().getHits()) {
            Map<String, HighlightField> highlightFields = hit.getHighlightFields();
            HighlightField highlightField = highlightFields.get("article_content");
            // 处理高亮结果
        }

        client.close();
    }
}

在Java代码中，同样通过matchQuery构建查询，HighlightBuilder设置高亮，topHits聚合获取前5条结果。your_index_name需替换为实际索引名称，关键词需替换为实际要匹配的词。

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面试题：ElasticSearch中如何通过顶部命中聚合实现高亮数据提取

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