使用Java的MongoDB - GroupBy更多一列

import com.mongodb.MongoClient;
import com.mongodb.client.AggregateIterable;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;

import java.util.Arrays;

public class MongoDBGroupByExample {
    public static void main(String[] args) {
        // 连接MongoDB数据库
        MongoClient mongoClient = new MongoClient("localhost", 27017);
        MongoDatabase database = mongoClient.getDatabase("mydb");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        // 构建GroupBy操作的聚合管道
        Document groupByFields = new Document("_id", "$field1");
        groupByFields.put("total", new Document("$sum", "$field2"));
        Document groupByStage = new Document("$group", groupByFields);
        AggregateIterable<Document> result = collection.aggregate(Arrays.asList(groupByStage));

        // 遍历结果
        for (Document document : result) {
            System.out.println(document.toJson());
        }

        // 关闭连接
        mongoClient.close();
    }
}