如何将Mango DB聚合(展开、匹配和投影)查询转换为java代码

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

import java.util.Arrays;

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

        // 构建聚合查询管道
        Document matchStage = new Document("$match", new Document("age", new Document("$gte", 18)));
        Document groupStage = new Document("$group", new Document("_id", "$gender").append("count", new Document("$sum", 1)));
        Document sortStage = new Document("$sort", new Document("count", -1));
        Document limitStage = new Document("$limit", 5);

        // 执行聚合查询
        Iterable<Document> results = collection.aggregate(Arrays.asList(matchStage, groupStage, sortStage, limitStage));

        // 处理查询结果
        for (Document result : results) {
            System.out.println(result.toJson());
        }

        // 关闭数据库连接
        mongoClient.close();
    }
}