Elasticsearch分析聚合介绍了分析聚合的REST命令，这篇博客介绍一下如何使用Java API。

一、准备数据

测试数据请参考我的上一篇博客:Elasticsearch分析聚合。

二、需求

查询title中包含关键字”程序”的文档，统计查询按编程语言分组，统计每组的文档数量。

三、REST命令行

REST命令行如下，有三部分，query查询所有title中包含关键词程序的文档，size指定返回结果中文档数量，其值为0只返回聚合的结果，aggs部分通过language字段进行分组。

GET books/_search
{
    "query": {
        "match": {
            "title": "程序" 
        }
    },
    "size": 0,
    "aggs": {
        "per_count": {
            "terms": {
                "field": "language"
            }
        }
    }
}

查询结果如下:

{
   "took": 5,
   "timed_out": false,
   "_shards": {
      "total": 5,
      "successful": 5,
      "failed": 0
   },
   "hits": {
      "total": 2,
      "max_score": 0,
      "hits": []
   },
   "aggregations": {
      "per_count": {
         "doc_count_error_upper_bound": 0,
         "sum_other_doc_count": 0,
         "buckets": [
            {
               "key": "java",
               "doc_count": 1
            },
            {
               "key": "javascript",
               "doc_count": 1
            }
         ]
      }
   }
}

四、聚合的JAVA API

        //创建TransportClient对象
        client=EsUtils.getEsClient();
        QueryBuilder matchQuery = QueryBuilders.matchQuery("title", "程序");
        AbstractAggregationBuilder aggregation = AggregationBuilders.terms("per_count").field("language");
        SearchResponse response = client.prepareSearch("books").setTypes("IT")
        .setQuery(matchQuery)
        .addAggregation(aggregation)
        .execute()
        .actionGet();
        SearchHits hits = response.getHits();
        for(SearchHit hit:hits){
            System.out.println("id:"+hit.getId()+"\ttitle:"+hit.getSource().get("title"));
        }
        Terms terms = response.getAggregations().get("per_count");
        List<Bucket> buckets = terms.getBuckets();
        for(Bucket bucket:buckets){
            System.out.println(bucket.getKey()+"----"+bucket.getDocCount());
        }
        client.close();

运行结果:

id:2    title:Java程序性能优化
id:5    title:JavaScript高级程序设计
java----1
javascript----1

五、更多聚合操作

Bucket aggregations

Metrics aggregations