Specifying a Custom Datetime Format When Serializing with JSON.Net

Specifying a custom DateTime format when serializing with Json.Net

You are on the right track. Since you said you can't modify the global settings, then the next best thing is to apply the JsonConverter attribute on an as-needed basis, as you suggested. It turns out Json.Net already has a built-in IsoDateTimeConverter that lets you specify the date format. Unfortunately, you can't set the format via the JsonConverter attribute, since the attribute's sole argument is a type. However, there is a simple solution: subclass the IsoDateTimeConverter, then specify the date format in the constructor of the subclass. Apply the JsonConverter attribute where needed, specifying your custom converter, and you're ready to go. Here is the entirety of the code needed:

class CustomDateTimeConverter : IsoDateTimeConverter
{
    public CustomDateTimeConverter()
    {
        base.DateTimeFormat = "yyyy-MM-dd";
    }
}

If you don't mind having the time in there also, you don't even need to subclass the IsoDateTimeConverter. Its default date format is yyyy'-'MM'-'dd'T'HH':'mm':'ss.FFFFFFFK (as seen in the source code).

Supporting multiple custom DateTime formats when deserializing with Json.Net

If you want to handle multiple possible date formats, you will need to make a custom JsonConverter which can accept multiple format strings and try them all until one succeeds. Here is a simple example:

class MultiFormatDateConverter : JsonConverter
{
    public List<string> DateTimeFormats { get; set; }
    
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(DateTime) || objectType == typeof(DateTime?);
    }
    
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        string dateString = (string)reader.Value;
        if (dateString == null) 
        {
            if (objectType == typeof(DateTime?))
                return null;
                
            throw new JsonException("Unable to parse null as a date.");
        }
        DateTime date;
        foreach (string format in DateTimeFormats)
        {
            // adjust this as necessary to fit your needs
            if (DateTime.TryParseExact(dateString, format, CultureInfo.InvariantCulture, DateTimeStyles.None, out date))
                return date;
        }
        throw new JsonException("Unable to parse \"" + dateString + "\" as a date.");
    }
    
    public override bool CanWrite
    {
        get { return false; }
    }
    
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

Then you can add it to your settings like this:

var settings = new JsonSerializerSettings();
settings.DateParseHandling = DateParseHandling.None;
settings.Converters.Add(new MultiFormatDateConverter 
{ 
    DateTimeFormats = new List<string> { "yyyyMMddTHHmmssZ", "yyyy-MM-ddTHH:mm" } 
});

Fiddle: https://dotnetfiddle.net/vOpMEY

Use JSON.net to serialize yyyyMMdd formatted date without quotes

You'll have to create your own JsonConverter because the one that comes out-of-the-box writes values as string and strings are always serialized with quotes...

You can copy the code of IsoDateTimeConverter and change it to write the value as an int.

How to force a single property to format as a Date and not a Date time when serializing

It looks like a custom converter applied using the JsonConverter attribute can do what you want. The following is sample code from the linked article:

Converter:

public class DateTimeOffsetJsonConverter : JsonConverter<DateTimeOffset>
{
    public override DateTimeOffset Read(
        ref Utf8JsonReader reader,
        Type typeToConvert,
        JsonSerializerOptions options) =>
            DateTimeOffset.ParseExact(reader.GetString(),
                "MM/dd/yyyy", CultureInfo.InvariantCulture);

    public override void Write(
        Utf8JsonWriter writer,
        DateTimeOffset dateTimeValue,
        JsonSerializerOptions options) =>
            writer.WriteStringValue(dateTimeValue.ToString(
                "MM/dd/yyyy", CultureInfo.InvariantCulture));
}

Applied using attribute:

public class WeatherForecastWithConverterAttribute
{
    [JsonConverter(typeof(DateTimeOffsetJsonConverter))]
    public DateTimeOffset Date { get; set; }
    public int TemperatureCelsius { get; set; }
    public string Summary { get; set; }
}

JSON Date and DateTime serialisation in c# & newtonsoft

As I mentioned in a comment, there is no standard date representation in JSON. The ISO8601 is the de-facto standard, ie most people started using this some years ago. ISO8601 does not require milliseconds. If the other endpoint requires them, it's violating the defacto standard.

Json.NET uses IOS8601 since version 4.5. The current one is 10.0.3. The following code :

JsonConvert.SerializeObject(DateTime.Now)

returns

"2017-09-08T19:01:55.714942+03:00"

On my machine. Notice the timezone offset. That's also part of the standard. Z means UTC.

You can specify your own time format, provided it's the correct one. In this case, it should be yyyy-MM-ddTHH:mm:ss.fffZ. Notice the fff for milliseconds and HH for 24-hour.

The following code

var settings=new JsonSerializerSettings{DateFormatString ="yyyy-MM-ddTHH:mm:ss.fffZ"};
var json=JsonConvert.SerializeObject(DateTime.Now,settings);

returns

"2017-09-08T19:04:14.480Z"

The format string does not force a timezone translation. You can tell Json.NET to treat the time as Local or Utc through the DateTimeZoneHandling setting :

var settings=new JsonSerializerSettings{
                              DateFormatString ="yyyy-MM-ddTH:mm:ss.fffZ",
                              DateTimeZoneHandling=DateTimeZoneHandling.Utc};
var json=JsonConvert.SerializeObject(DateTime.Now,settings);

Returns :

"2017-09-08T16:08:19.290Z"

UPDATE

As Matt Johnson explains, Z is just a literal, while K generates either Z or an offset, depending on the DateTimeZoneHandling setting.

The format string yyyy-MM-ddTH:mm:ss.fffK with DateTimeZoneHandling.Utc :

var settings=new JsonSerializerSettings{
                              DateFormatString ="yyyy-MM-ddTH:mm:ss.fffK",
                              DateTimeZoneHandling=DateTimeZoneHandling.Utc};
var json=JsonConvert.SerializeObject(DateTime.Now,settings);

Will return :

2017-09-11T9:10:08.293Z

Changing to DateTimeZoneHandling.Utc will return

2017-09-11T12:15:12.862+03:00

Which, by the way is the default behaviour of Json.NET, apart from the forced millisecond precision.

Finally, .NET doesn't have a Date-only type yet. DateTime is used for both dates and date+time values. You can get the date part of a DateTime with the DateTime.Date property. You can retrieve the current date with DateTime.Today.

Time of day is represented by the Timespan type. You can extract the time of day from a DateTime value with DateTime.TimeOfDay. Timespan isn't strictly a time-of-day type as it can represent more than 24 hours.

What was that yet?

Support for explicit Date, TimeOfDay is comming through the CoreFX Lab project. This contains "experimental" features that are extremely likely to appear in the .NET Runtime like UTF8 support, Date, String, Channles. Some of these already appear as separate NuGet packages.

One can use the System.Time classes already, either by copying the code or adding them through the experimental NuGet source

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