SpringBoot + ElasticSearch聚合搜索

ElasticSearch的构造是：

1. 如果要使用where过滤数据，首先要构造RangeQuery或者BooleanQuery等专门用于过滤的QueryBuilder
2. 如果要对数据进行分组，则构造AggregationBuilder，如果在这个基础上还要构造count, sum等，则需要利用subAggregation。

例如对时间进行按天聚合后再统计每天的数据计数，代码如下：

public class CLAPResult {
    /**
     * timeStamp 请求完成时的时间戳，Unix 时间戳
     */
//    @Field(type = FieldType.Date)
    public String timeStamp;

    public Long count;

}

        public List<CLAPResult> countByDay(Date start, Date end) {

        // 类似SQL语句
        // select date(timeStamp) as 日期, count(*) as 总数
        // from performances
        // where timeStamp between start and end
        // group by 日期
        // order by 日期
        List<CLAPResult> ret = new ArrayList<>();
        SearchRequest searchRequest = new SearchRequest(INDEX_NAME);
        SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();

        // count(xxx)，如果要 count(distinct)，使用 .cardinality 替代 count
        ValueCountAggregationBuilder count = AggregationBuilders.count("总数").field("_id");

        // timeStamp between 开始时间 and 结束时间
        RangeQueryBuilder rangeQuery = QueryBuilders.rangeQuery("timeStamp").gte(start).lte(end);

        AggregationBuilder group = AggregationBuilders  // group by
                .dateHistogram("日期")
                .fixedInterval(DateHistogramInterval.days(1))
                .minDocCount(0)  // 返回空桶
                .field("timeStamp")
//                .offset("-8h")
                .format("yyyy-MM-dd")
                .subAggregation(count);
        sourceBuilder.query(rangeQuery).aggregation(group).sort("timeStamp", SortOrder.DESC);

        searchRequest.source(sourceBuilder);
        RequestOptions options = RequestOptions.DEFAULT;
        try {
            SearchResponse searchResponse = elasticsearchClient.search(searchRequest, options);

            Aggregations aggregations = searchResponse.getAggregations();
            Histogram histogram = aggregations.get("日期");
            List<? extends Histogram.Bucket> buckets = histogram.getBuckets();
            for (Histogram.Bucket bucket : buckets) {
                CLAPResult item = new CLAPResult();
                item.timeStamp = bucket.getKeyAsString();
                Aggregation aggregation = bucket.getAggregations().get("总数");
                if (aggregation instanceof ParsedValueCount) {
                    ParsedValueCount valueCount = (ParsedValueCount) aggregation;
                    item.count = valueCount.getValue();
                }
                ret.add(item);
            }
        } catch (IOException e) {
            Log.debug("PagePerformanceServiceImpl.findByUrl() 错误: " + e.getMessage());
        }

        return ret;
    }