use mockdb
db.mockcoll.createIndex({"flag":1})
db.mockcoll.getIndexes()

public interface MongoCons {

    String mockdbName = "mockdb";
    String mockcollName = "mockcoll";
    
    static MongoCollection<Document> getCollection(MongoTemplate mongoTemplate){
        MongoDatabase mongoDatabase = mongoTemplate.getMongoDbFactory().getMongoDatabase(mockdbName);
        MongoCollection<Document> collection = mongoDatabase.getCollection(mockcollName);
        return collection;
    }
    
}

@Component
public class MongoBulkDao {

    private Logger logger = LoggerFactory.getLogger(MongoBulkDao.class);
    @Autowired
    private MongoTemplate mongoTemplate;

    public void addOrUpdate(List<String> dataList) {
        try {
            MongoCollection<Document> collection = MongoCons.getCollection(mongoTemplate);

            List<WriteModel<Document>> list = new ArrayList<>();

            Iterator<String> iterator = dataList.iterator();
            String next = null;
            while (iterator.hasNext()) {
                next = iterator.next();
                BasicDBObject filter = new BasicDBObject().append("flag", next);
                BasicDBObject update = new BasicDBObject().append("$set", new BasicDBObject().append("flag", next));

                UpdateOneModel<Document> um = new UpdateOneModel<Document>(filter, update,
                        new UpdateOptions().upsert(true));
                list.add(um);
                iterator.remove();
            }

            collection.bulkWrite(list, new BulkWriteOptions().ordered(false));
        } catch (Exception e) {
            logger.error("",e);
        }
    }