如何在java中实现spring数据聚合中的$size

import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.aggregation.Aggregation;
import org.springframework.data.mongodb.core.aggregation.AggregationResults;
import org.springframework.data.mongodb.core.aggregation.TypedAggregation;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;

import java.util.List;

public class Main {
    public static void main(String[] args) {
        MongoTemplate mongoTemplate = new MongoTemplate(); // 初始化MongoTemplate

        // 创建聚合查询条件
        Criteria criteria = Criteria.where("arrayField").exists(true);
        TypedAggregation aggregation = Aggregation.newAggregation(
                Aggregation.match(criteria),
                Aggregation.project().and("arrayField").size().as("arraySize")
        );

        // 执行聚合查询
        AggregationResults<ResultClass> results = mongoTemplate.aggregate(aggregation, "collectionName", ResultClass.class);
        List<ResultClass> resultList = results.getMappedResults();

        // 处理查询结果
        for (ResultClass result : resultList) {
            int arraySize = result.getArraySize();
            System.out.println("Array size: " + arraySize);
        }
    }

    // 定义结果类
    public static class ResultClass {
        private int arraySize;

        public int getArraySize() {
            return arraySize;
        }

        public void setArraySize(int arraySize) {
            this.arraySize = arraySize;
        }
    }
}