要按字段名称对 Elasticsearch 进行聚合，可以使用 Elasticsearch 的聚合功能来实现。下面是一个示例代码，演示了如何使用 Elasticsearch 的 Java 客户端进行按字段名称聚合：

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.terms.Terms;
import org.elasticsearch.search.builder.SearchSourceBuilder;

import java.io.IOException;

public class ElasticsearchAggregationExample {
    public static void main(String[] args) {
        // 创建 Elasticsearch 客户端
        RestHighLevelClient client = new RestHighLevelClient(
                RestClient.builder(new HttpHost("localhost", 9200, "http")));

        try {
            // 创建搜索请求
            SearchRequest searchRequest = new SearchRequest("your_index_name");
            SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();

            // 设置查询条件
            searchSourceBuilder.query(QueryBuilders.matchAllQuery());

            // 添加聚合操作，按字段名称进行聚合
            searchSourceBuilder.aggregation(AggregationBuilders.terms("your_aggregation_name")
                    .field("your_field_name"));

            // 将搜索源设置到搜索请求中
            searchRequest.source(searchSourceBuilder);

            // 执行搜索请求
            SearchResponse searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);

            // 获取聚合结果
            Terms termsAggregation = searchResponse.getAggregations().get("your_aggregation_name");
            for (Terms.Bucket bucket : termsAggregation.getBuckets()) {
                String fieldValue = bucket.getKeyAsString();
                long count = bucket.getDocCount();
                System.out.println("Field: " + fieldValue + ", Count: " + count);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // 关闭客户端连接
            try {
                client.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

在上述代码中，你需要将 your_index_name 替换为你要进行聚合的索引名称，your_field_name 替换为你要按其进行聚合的字段名称。运行代码后，你将得到按字段名称进行聚合的结果，并输出每个字段值和对应的文档数量。