Mongodb Timestamp Output Format returns "$numberLong" Object when I want to get the unix time in millis

medTech :

I develop a Spring Application which saves JSON in MongoDb. The client is able to search for data with entering a time interval begin and end. To be able to use regex (lte and gte) to get the data from the database I save the Time as UnixTimeStamp:

 "TimeStamp": {
                "StartTime": 1549371540000,
                "EndTime" : 1549371540000,
                "StartTimeZone":"Europe/Berlin",
                "EndTimeZone":"Europe/Berlin"
            }

The filtering works but I get the following as a result:

"TimeStamp": {
                    "StartTimeZone": "Europe/Berlin",
                    "EndTimeZone": "Europe/Berlin",
                    "EndTime": {
                        "$numberLong": "1549371540000"
                    },
                    "StartTime": {
                        "$numberLong": "1549371540000"
                    }
                }

Is it possible to just get the key-value pair instead of the StartTime Object with the $numberLong key? I was also thinking about saving the time aso Iso format with yyyy_mm_ddTHH:MM:SS+-Offset

But as far as i know I can just the regex to filter the time in this format. Dealing with the time is an essential part of the project and I want to make shure that I treat this part in a best practice way.

EDIT: In my code I to

for (Document doc : collection.find(query).projection(Projections.include(projectionList))) {
            //Save the query result as a List of JSON-Objects
            dataList.add(doc.toJson());
        }

to save the results as a list of jsons. I know that the toJson method is deprecated but I wasn't able to find a way to convert the document into a JSON notation.

Vijay Rajpurohit :

Is it possible to just get the key-value pair instead of the StartTime Object with the $numberLong key?

JsonWriterSettings settings = JsonWriterSettings.builder()
        .int64Converter((value, writer) -> writer.writeNumber(value.toString())).build();

document.toJson(settings); // The output would contain simple long value