How to convert this MongoDB Aggregation Pipeline to Java Spring Boot code?

Question

[
  {
    "$match": {
      "userId": "user_1"
    }
  },
  {
    "$lookup": {
      "from": "Events",
      "localField": "eventId",
      "foreignField": "_id",
      "as": "eventDetails"
    }
  },
  {
    "$addFields": {
      "eventName": { "$ifNull": [{ "$arrayElemAt": ["$eventDetails.name", 0] }, "Unknown"] },
      "date": { "$ifNull": [{ "$arrayElemAt": ["$eventDetails.date", 0] }, "Unknown"] },
      "location": { "$ifNull": [{ "$arrayElemAt": ["$eventDetails.location", 0] }, "Unknown"] }
    }
  },
  {
    "$group": {
      "_id": "$eventId",
      "eventName": { "$first": "$eventName" },
      "date": { "$first": "$date" },
      "location": { "$first": "$location" },
      "tickets": { "$addToSet": "$_id" },
      "count": { "$sum": 1 }
    }
  }
]

I am not sure how to convert this to Java code. Can someone help me with it?
The code conversion provided by MongoDB Atlas doesn't seem to be reliable.
I want to convert this to Java Code using Aggregations.