如何在Java中将Elasticsearch聚合的结果打印为JSON字符串？

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

SearchRequest searchRequest = new SearchRequest("index_name");
SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();

// 添加聚合查询
sourceBuilder.aggregation(AggregationBuilders.terms("agg_name").field("field_name"));

searchRequest.source(sourceBuilder);

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

Aggregations aggregations = searchResponse.getAggregations();
Terms agg = aggregations.get("agg_name");

List<? extends Terms.Bucket> buckets = agg.getBuckets();
for (Terms.Bucket bucket : buckets) {
    String key = bucket.getKeyAsString();
    long docCount = bucket.getDocCount();

    // 打印聚合结果
    System.out.println("Key: " + key + ", Doc Count: " + docCount);
}

// 将聚合结果转换为JSON字符串
String jsonResult = aggregations.toString();
System.out.println("JSON Result: " + jsonResult);