Java总是比python或javascript更冗长一些，但我是这样做的：因为我的编辑器匹配大括号和方括号，所以我发现将查询构造为JSON，然后将其转换为所需的Document对象管道更容易。

import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;

import com.mongodb.client.ClientSession;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoCursor;
import com.mongodb.client.AggregateIterable;

import org.bson.*;

import java.util.Arrays;

import java.util.ArrayList;
import java.util.List;
import java.util.Date;
import java.text.SimpleDateFormat;
import java.util.Map;
import java.util.HashMap;

import java.math.BigDecimal;

public class agg4 {

    private MongoClient mongoClient;
    private MongoDatabase db;
    private MongoCollection<Document> coll;

    private static class StageHelper {
        private StringBuilder txt;
        public StageHelper() {
            this.txt = new StringBuilder();
        }
        public void add(String expr, Object ... subs) {
            expr.replace("'", "\""); // This is the helpful part.
            if(subs.length > 0) {
                expr = String.format(expr, subs);  // this too
            }
            txt.append(expr);
        }       
        public Document fetch() {
            return Document.parse(txt.toString());
        }
    }
        
    private List<Document> makePipeline() {
        List<Document> pipeline = new ArrayList<Document>();    

        StageHelper s = new StageHelper();

        // It is left as an exercise to add all the other individual fields
        // that need to be matched and properly pass them in, etc.
        String val_aC = "AB";
        String val_aI = "ABCD";
        s.add(" {'$match': {'aC':'%s','aI':'%s'}}", val_aC, val_aI );
        pipeline.add(s.fetch());
        
        s = new StageHelper();
        // This is the meat.  Find seqNo = 4.  Since I suspect seqNo is
        // unique, it does no extra good to filter the array to just an array
        // array of one; changing the array of 1 (if found of course) to a
        // *single* object has more utility, hence use of $arrayElemAt:
        s.add(" {'$project': {'transaction': {'$arrayElemAt': [ ");
        s.add("   {'$filter': {'input': '$transactions', ");
        s.add("                'cond': {'$eq':['$$this.seqNo', 4]} ");
        s.add("   }}, 0]} ");
        s.add(" }}");

        pipeline.add(s.fetch());
        
        s = new StageHelper();
        // If seqNo = 4 could not be found, transaction will be unset so
        // use the following to exclude that doc.
        s.add(" {'$match': {'transaction': {'$exists': true}}} ");
        pipeline.add(s.fetch());
        
        return pipeline;
    }
        
    private void doAgg() {
        try {
            List<Document> pipeline = makePipeline();
            AggregateIterable<Document> output = coll.aggregate(pipeline);
            MongoCursor<Document> iterator = output.iterator();
            while (iterator.hasNext()) {
                    Document doc = iterator.next();
            }
            
        } catch(Exception e) {
            System.out.println("some fail: " + e);
        }
    }

    public static void main(String[] args) {
        (new agg4()).go(args);
    }

    public void go(String[] args) {
        try {
            Map params = new HashMap();

            String host = "mongodb://localhost:37017/?replicaSet=rs0";
            String dbname = "testX";
            String collname = "foo";

            mongoClient = MongoClients.create(host);
            db = mongoClient.getDatabase(dbname);
            coll = db.getCollection(collname, Document.class);

            doAgg();

        } catch(Exception e) {
            System.out.println("epic fail: " + e);
            e.printStackTrace();
        }
    }

如果您使用的是Java 13或更高版本，则String的文本块会使操作更加简单：

String s = """
        {'$project': {'transaction': {'$arrayElemAt': [ 
            {'$filter': {'input': '$transactions',
                         'cond': {'$eq':['$$this.seqNo', 4]}
            }}, 0]}
        }}
    """;
    pipeline.add(s.fetch());