using System;

using System.Reflection;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Serialization;

public class Program

{

    public static void Main()

    {

        try

        {

            var person = new Person

            {

                FirstName = "George",

                LastName = "Washington"

            };

            var settings = new JsonSerializerSettings

            {

                ContractResolver = new CustomResolver()

            };

            var serialized = JsonConvert.SerializeObject(person, settings);

            var expected = @"{""FirstName"":""George"",""LastName"":""WASHINGTON""}";

            Assert.Equal(expected, serialized);

            Console.WriteLine(serialized);

        }

        catch (Exception ex)

        {

            Console.WriteLine(ex.GetType().Name + ": " + ex.Message);

        }

    }

}

​

public class CustomResolver : DefaultContractResolver

{

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)

    {

        JsonProperty prop = base.CreateProperty(member, memberSerialization);

        if (prop.DeclaringType == typeof(Person) && prop.UnderlyingName == "LastName")

        {

            prop.Converter = new AllCapsConverter();

        }

        return prop;

    }

}

​

public class Person

{

    public string FirstName { get; set; }

    public string LastName { get; set; }

}

​

public class AllCapsConverter : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

        return objectType == typeof(string);

    }

​

    public override bool CanRead 

    {

        get { return false; }

    }

​

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

    {

        throw new NotSupportedException();

    }

​

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

    {

        var str = value as string;

        var upper = str.ToUpperInvariant();

        JToken j = JToken.FromObject(upper);

        j.WriteTo(writer);

    }

}

​

public class Assert

{

    public static void Equal(string expected, string actual)

    {

        if (!string.Equals(expected, actual))

            throw new Exception("Strings are not equal. Expected \"" + expected + "\" but got \"" + actual + "\"");

    }

}

​