用restHighLevelClient 实现

使用 `restHighLevelClient` 来实现 Elasticsearch 的聚合查询需要编写 Java 代码。首先，你需要创建一个 `RestHighLevelClient` 实例，然后利用它的 `search()` 方法执行查询，并指定一个 `SearchRequest` 对象，里面包含了查询条件和聚合设置。下面是一个简单的示例，假设你已经有一个初始化好的 `RestHighLevelClient` 变量 `client`：

// 导入必要的依赖库
import org.elasticsearch.action.search.SearchRequest;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.index.query.HumanBuilders;
import org.elasticsearch.search.builder.SearchSourceBuilder;
import org.elasticsearch.search.aggregations.AggregationBuilders;

// ... (已初始化的client)

// 构建 SearchRequest
SearchRequest searchRequest = new SearchRequest("your_index");
SearchSourceBuilder searchSource = new SearchSourceBuilder();
searchSource.aggregation(AggregationBuilders.terms("keyword_values")
        .field("keywords.a")) // 选择 a 字段进行聚合
        .size(0); // 设置大小为0，因为我们只关心聚合结果

searchRequest.source(searchSource);

// 执行请求并获取结果
Response response = client.search(searchRequest, RequestOptions.DEFAULT);
SearchResponse searchResult = response.getSearchResponse();

// 提取聚合结果
Aggregations aggregations = searchResult.getAggregations();
List<Terms.Bucket> buckets = aggregations.get("keyword_values").getBuckets();
for (Terms.Bucket bucket : buckets) {
    String key = bucket.getKeyAsString(); // 获取键值
    long docCount = bucket.docCount(); // 获取文档计数
    System.out.println("Key: " + key + ", Doc Count: " + docCount);
}