[转]Newtonsoft JSON how to dynamically change the date format?

本文转自：http://www.howtobuildsoftware.com/index.php/how-do/cg8K/jsonnet-newtonsoft-json-how-to-dynamically-change-the-date-format

I'm using Newtonsoft JSON Serializer and it's great and super fast but I'd like to do a bit more with it. I'm not sure it's possible as all the search I've done comes up to nothing. What I would like is to be able to truncate empty time, so when it's display 2014-01-01 00:00:00.000 I just want 2014-01-01 at the end, so basically cut the entire time when they're all zeros. For now I use this piece of code:

DataTable dt = loadData();

// encode the string with Newton JSON.Net
string output = JsonConvert.SerializeObject(dt,
    new JsonSerializerSettings
    {
        ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
        Formatting = Newtonsoft.Json.Formatting.None,
        DateFormatString = "yyyy-MM-dd HH:mm:ss"
    });

Is there a way to format these dates without the time (only when they are all zeros) without affecting the performance?

Best How To :

You can do this with a custom JsonConverter:

class CustomDateConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(DateTime));
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        DateTime date = (DateTime)value;
        string format = "yyyy-MM-dd HH:mm:ss";
        if (date.Hour == 0 &&
            date.Minute == 0 &&
            date.Second == 0 &&
            date.Millisecond == 0)
        {
            format = "yyyy-MM-dd";
        }
        writer.WriteValue(date.ToString(format));
    }

    public override bool CanRead
    {
        get { return false; }
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

Demo:

class Program
{
    static void Main(string[] args)
    {
        List<DateTime> dates = new List<DateTime>
        {
            DateTime.Now,
            DateTime.Today
        };

        JsonSerializerSettings settings = new JsonSerializerSettings
        {
            ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
            Formatting = Newtonsoft.Json.Formatting.None,
            Converters = new List<JsonConverter> { new CustomDateConverter() }
        };

        string json = JsonConvert.SerializeObject(dates, settings);

        Console.WriteLine(json);
    }
}

Output:

["2014-06-11 11:56:28","2014-06-11"]