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。