JsonSerializer：区分DateTime对象的种类

Question

I have a dynamic object that contains dates (among other data).

Some of these dates have Kind UTC and others have Kind Local, eg:

var dynamicObject = new 
{
     utcDate = DateTime.UtcNow,    //This one has Kind = DateTimeKind.Utc
     localDate = DateTime.Now      //This one has Kind = DateTimeKind.Local
}

And then I have a JsonSerializer that works as follows:

var isoDateTimeConverter = new IsoDateTimeConverter();
isoDateTimeConverter.DateTimeFormat = "yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'";
                                            //                       ^
                                            //                  Notice this

var serializerSettings = new JsonSerializerSettings();
SerializerSettings.Converters.Add(isoDateTimeConverter);

var response = context.HttpContext.Response;
var writer = new JsonTextWriter(response.Output) { Formatting = Formatting };

var serializer = JsonSerializer.Create(serializerSettings);
serializer.Serialize(writer, dynamicObject);

writer.Flush();

Which creates a JSON string as this:

{
     "utcDate":"2019-05-02T19:52:20Z",
     "localDate":"2019-05-02T15:52:20Z"
}

This is expected because of how my isoDateTimeConverter is currently defined.

But I'd like to serialize as follows:

{
     "utcDate":"2019-05-02T19:52:20Z",
     "localDate":"2019-05-02T15:52:20"    // <--- no Z
}

Meaning that I'd like to add a 'Z' only when the Kind of the DateTime is Utc .

Is this possible with IsoDateTimeConverter and/or JsonSerializerSettings ?

Answer 1

I would either use IsoDateTimeConverter without setting the DateTimeFormat , which outputs the full DateTime value, with fractions of seconds, and a "Z" if the DateTimeKind is UTC or a time zone offset in "+-HH:mm" format if Local (and the empty string if None ).

Otherwise, the K specifier will format the value as you desire, appending the same values for the offset from UTC.

using System;
using Newtonsoft.Json;
using Newtonsoft.Json.Converters;

public class Program
{
    public static void Main(string[] args)
    {
        var dynamicObject = new
        {
            utcDate = DateTime.UtcNow, //This one has Kind = DateTimeKind.Utc
            localDate = DateTime.Now //This one has Kind = DateTimeKind.Local
        }

        ;
        var isoDateTimeConverter = new IsoDateTimeConverter();
        isoDateTimeConverter.DateTimeFormat = "yyyy'-'MM'-'dd'T'HH':'mm':'ssK";
        var serializerSettings = new JsonSerializerSettings();
        serializerSettings.Converters.Add(isoDateTimeConverter);
        var s = new System.Text.StringBuilder();
        using (var w = new System.IO.StringWriter(s))
        using (var writer = new JsonTextWriter(w)
                   {Formatting = Formatting.Indented})
        {
            var serializer = JsonSerializer.Create(serializerSettings);
            serializer.Serialize(writer, dynamicObject);
            writer.Flush();
        }

        Console.WriteLine(s.ToString());
    }
}

dotnetfiddle .

The ISO 8601 format allows for many variations of dates and times, to arbitrary precision. From Wikipedia's article on ISO 8601 :

There is no limit on the number of decimal places for the decimal fraction. However, the number of decimal places needs to be agreed to by the communicating parties.

Answer 2

A few things:

• You should not serialize DateTime values with DateTimeKind.Local values without an offset. Since it's local time, the local offset should be provided. Otherwise the receiver may interpret the value in their local time - which may be different than the sender's.

• The K specifier , when paired with DateTimeStyles.RoundTripKind , properly serializes in all supported ISO 8601 formats:

  • DateTimeKind.Utc gets serialized with a Z appended
  • DateTimeKind.Local gets serialized with the local offset appended, such as -07:00
  • DateTimeKind.Unspecified gets serialized without anything appended

• These are the defaults already given by the IsoDateTimeConverter , which is the default converter for DateTime values. Thus, in most cases you don't need to specify any converter at all.

• Fractional seconds to any length are allowed by ISO 8601. The RoundTripKind style gives 7 decimals because that is the precision supported by DateTime . Client side code in JavaScript generally supports only milliseconds, so extra decimals would be truncated when parsed on the client.

• If you must truncate decimals, then:

   isoDateTimeConverter.DateTimeFormat = "yyyy-MM-dd'T'HH:mm:ssK"; 

• If you feel like you must truncate offsets for local time, the better way would be to set DateTimeKind.Unspecified using DateTime.SpecifyKind before serialization.

• If you feel like you should change this globally , then you would create your own JsonConverter . You could inherit from the IsoDateTimeConverter and override the ReadJson and WriteJson methods, or you could just start directly from JsonConverter . Since I don't recommend this approach, I won't add one here.