db.messages.aggregate([
    { $match: { _id: {$exists: true} },
    { $sort: { _id: 1 } }, // here you can sort using other field
    { $group: {
        _id: null,
    messagesCount: { $sum: 1 },
    allMessages: {
      $push: '$$ROOT'
    }
  } }
  { $project: {
    _id: 0,
    messagesCount: 1,
    messagesPage: {
      $slice: ['$allMessages', 0, 30] //pageNo=0, pageSize=30
    }
  } }
])

MatchOperation matchOperation = new MatchOperation(Criteria.where("_id").exists(true));
SortOperation sortOperation = new SortOperation(new Sort(Sort.Direction.DESC, "_id"));
//HOW DO I TRANSLATE THESE TWO IN JAVA CODE?
GroupOperation groupOperation = Aggregation.group()....**???**
ProjectionOperation projectOperation = Aggregation.project()...**???**


mongoTemplate.aggregate(
            newAggregation(matchOperation, sortOperation, groupOperation, projectOperation), "messages", MessagesSortedAndPaginated.class);

public class MessagesSortedAndPaginated {
    private long totalCount;
    private List<Message> messagesPage;
}

@Document(collection = "messages")
 public @Data class Message implements Serializable {

        private static final long serialVersionUID = 1L;

        @Id
        private String id;
    ...

GroupOperation groupOperation = Aggregation.group().count().as("messagesCount").push(Aggregation.ROOT).as("messagesPage");
ProjectionOperation projectOperation = Aggregation.project().andExpression("messagesCount").as("messagesPage")