java实现esGroupby查询

要在Java中实现ES的Group By查询，可以使用ES的Java客户端API。以下是一个简单的示例代码，它使用ES的Java API执行一个聚合查询并按指定字段进行分组：

import org.elasticsearch.action.search.SearchRequest;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.common.unit.TimeValue;
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.bucket.terms.Terms;
import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
import org.elasticsearch.search.builder.SearchSourceBuilder;

import java.io.IOException;

public class ESGroupByQuery {

    public static void main(String[] args) throws IOException {

        RestHighLevelClient client = new RestHighLevelClient(
                RestClient.builder(
                        new HttpHost("localhost", 9200, "http")));

        String index = "my-index";
        String fieldToGroupBy = "some-field";

        TermsAggregationBuilder aggregation =
                AggregationBuilders.terms("by_" + fieldToGroupBy).field(fieldToGroupBy);

        SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder()
                .query(QueryBuilders.matchAllQuery())
                .aggregation(aggregation)
                .size(0);

        SearchRequest searchRequest = new SearchRequest(index)
                .source(searchSourceBuilder)
                .scroll(new TimeValue(60000));

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

        SearchHits hits = searchResponse.getHits();

        Terms terms = searchResponse.getAggregations().get("by_" + fieldToGroupBy);

        for (Terms.Bucket bucket : terms.getBuckets()) {
            String fieldValue = bucket.getKeyAsString();
            long count = bucket.getDocCount();
            System.out.println(fieldValue + ": " + count);
        }

        client.close();
    }
}

在上面的示例中，我们使用了ES的Java API创建了一个名为“by_some-field”的聚合，该聚合将按“some-field”字段进行分组。我们还使用了“matchAllQuery”查询来检索所有文档，并将结果集大小设置为0，因为我们只需要聚合结果，而不需要实际的文档数据。

在执行查询后，我们可以使用ES的Java API检索聚合结果，并对每个分组打印出其数量。