Elasticsearch Aggregation 多个字段分组统计 Java API实现

现有索引数据：

index:school
type:student
---------------------------------------------------
{"grade":"1", "class":"1", "name":"xiao 1"}
{"grade":"1", "class":"1", "name":"xiao 2"}
{"grade":"1", "class":"2", "name":"xiao 3"}
{"grade":"1", "class":"2", "name":"xiao 4"}
{"grade":"1", "class":"2", "name":"xiao 5"}

Java分组统计年级和班级学生个数，如SQL: SELECT grade,class,count(1) FROM student GROUP BY grade,class;

package test;

import java.util.Iterator;
import java.util.Map;

import org.elasticsearch.action.search.SearchRequestBuilder;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.action.search.SearchType;
import org.elasticsearch.search.aggregations.Aggregation;
import org.elasticsearch.search.aggregations.AggregationBuilders;
import org.elasticsearch.search.aggregations.bucket.terms.StringTerms;
import org.elasticsearch.search.aggregations.bucket.terms.Terms.Bucket;
import org.elasticsearch.search.aggregations.bucket.terms.TermsBuilder;
import org.junit.Test;

import utils.NesUtils;

public class TestAggregation
{
    @Test
    public void testAggregation()
    {
        SearchRequestBuilder srb = NesUtils.getSearcher("school");
        srb.setTypes("student");
        srb.setSearchType(SearchType.COUNT);
        
        TermsBuilder gradeTermsBuilder = AggregationBuilders.terms("gradeAgg").field("grade");
        TermsBuilder classTermsBuilder = AggregationBuilders.terms("classAgg").field("class");
        
        gradeTermsBuilder.subAggregation(classTermsBuilder);
        
        srb.addAggregation(gradeTermsBuilder);
        
        SearchResponse sr = srb.execute().actionGet();
        
        Map<String, Aggregation> aggMap = sr.getAggregations().asMap();
        
        StringTerms gradeTerms = (StringTerms) aggMap.get("gradeAgg");
        
        Iterator<Bucket> gradeBucketIt = gradeTerms.getBuckets().iterator();
        
        while(gradeBucketIt.hasNext())
        {
            Bucket gradeBucket = gradeBucketIt.next();
            System.out.println(gradeBucket.getKey() + "年级有" + gradeBucket.getDocCount() +"个学生。");
            
            StringTerms classTerms = (StringTerms) gradeBucket.getAggregations().asMap().get("classAgg");
            Iterator<Bucket> classBucketIt = classTerms.getBuckets().iterator();
            
            while(classBucketIt.hasNext())
            {
                Bucket classBucket = classBucketIt.next();
                System.out.println(gradeBucket.getKey() + "年级" +classBucket.getKey() + "班有" + classBucket.getDocCount() +"个学生。");
            }
            System.out.println();
        }
        
    }
}

运行完成输出结果
---------------------------------------------------
1年级有5个学生。
1年级2班有3个学生。
1年级1班有2个学生。