Java Mongo:如何获取每个文档的最大值

import com.mongodb.MongoClient;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.model.Accumulators;
import com.mongodb.client.model.Aggregates;
import com.mongodb.client.model.Filters;
import org.bson.Document;

import java.util.Arrays;

public class JavaMongoExample {
    public static void main(String[] args) {
        // 创建MongoDB连接
        MongoClient mongoClient = new MongoClient("localhost", 27017);

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

        // 构建聚合管道
        Document groupBy = new Document("_id", null);
        groupBy.put("maxValue", new Document("$max", "$value"));
        Document groupStage = new Document("$group", groupBy);
        Iterable<Document> pipeline = Arrays.asList(groupStage);

        // 执行聚合操作
        Iterable<Document> result = collection.aggregate(pipeline);

        // 处理聚合结果
        for (Document document : result) {
            Double maxValue = document.getDouble("maxValue");
            System.out.println("Max value: " + maxValue);
        }

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