使用MongoDB Java驱动程序进行聚合的分组和求和

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 MongoDBAggregationExample {
    public static void main(String[] args) {
        // 连接到MongoDB数据库
        MongoClient mongoClient = new MongoClient("localhost", 27017);

        // 获取数据库和集合
        MongoDatabase database = mongoClient.getDatabase("mydb");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        // 构建聚合管道
        AggregateIterable<Document> iterable = collection.aggregate(Arrays.asList(
                new Document("$group", new Document("_id", "$category").append("total", new Document("$sum", "$quantity")))
        ));

        // 处理聚合结果
        for (Document document : iterable) {
            String category = document.getString("_id");
            int totalQuantity = document.getInteger("total");
            System.out.println("Category: " + category + ", Total Quantity: " + totalQuantity);
        }

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