以下是一个使用Java API从Elasticsearch查询中获取中间bucket的示例代码：

import org.elasticsearch.action.search.SearchRequest;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.search.aggregations.AggregationBuilders;
import org.elasticsearch.search.aggregations.bucket.MultiBucketsAggregation;
import org.elasticsearch.search.aggregations.bucket.terms.ParsedStringTerms;
import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
import org.elasticsearch.search.aggregations.metrics.Sum;
import org.elasticsearch.search.builder.SearchSourceBuilder;

import java.io.IOException;

public class ElasticsearchAggregationExample {
    public static void main(String[] args) {
        RestHighLevelClient client = new RestHighLevelClient(
                RestClient.builder("localhost:9200"));

        SearchRequest searchRequest = new SearchRequest("your_index_name");
        SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();

        // 构建terms aggregation
        TermsAggregationBuilder aggregation = AggregationBuilders
                .terms("by_category")
                .field("category.keyword")
                .subAggregation(AggregationBuilders.sum("total_sales").field("sales"));

        searchSourceBuilder.aggregation(aggregation);
        searchRequest.source(searchSourceBuilder);

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

            // 获取terms聚合的结果
            ParsedStringTerms terms = searchResponse.getAggregations().get("by_category");

            // 遍历获取每个bucket的key和sum值
            for (Terms.Bucket bucket : terms.getBuckets()) {
                String key = bucket.getKeyAsString();
                Sum sum = bucket.getAggregations().get("total_sales");
                double totalSales = sum.getValue();

                System.out.println("Category: " + key + ", Total Sales: " + totalSales);
            }

            client.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

在上述代码中，首先创建一个RestHighLevelClient对象，连接到Elasticsearch集群。然后构建一个SearchRequest对象，指定要查询的索引名称。使用SearchSourceBuilder构建查询条件，其中包括terms聚合和sum指标聚合。执行查询后，从SearchResponse对象中获取terms聚合的结果，并遍历每个bucket，获取key和sum值。

请根据自己的实际情况修改代码中的索引名称、字段名称等。