using System;

using System.Linq;

using System.Text;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var myObject = new MyModelClass("blablabla", "<>@%#^^@!%");

        string json = JsonConvert.SerializeObject(myObject, Formatting.Indented);

        Console.WriteLine(json);

    }

}

​

​

public class MyModelClass

{

    [JsonProperty("first_field")]

    public string FirstField { get; set; }

​

    [JsonIgnore]

    public string SecondField { get; set; }

    [JsonProperty("second_field")]

    private string UrlEncodedSecondField

    {

        get { return System.Web.HttpUtility.UrlEncode(SecondField); }

    }

    public MyModelClass(string first, string second)

    {

        FirstField = first;

        SecondField = second;

    }

}

​

​

​

// System.Web is not accessible in .Net Fiddle, so this is a shim to stand in for the HttpUtility class.

// This is for demonstration purposes only.  Do not use this in production code; use the real System.Web.HttpUtility class instead.

namespace System.Web

{

    public static class HttpUtility

    {

        public static string UrlEncode(string url)

        {

            StringBuilder sb = new StringBuilder();

            if (!string.IsNullOrEmpty(url))

            {

                foreach (char c in url)

                {

                    if (IsUrlSafeChar(c))

                        sb.Append(c);

                    else

                    {

                        sb.Append('%');

                        sb.Append(((int)c).ToString("X2"));

                    }

                }

            }

            return sb.ToString();

        }

        private static bool IsUrlSafeChar(char c)

        {

            char[] safePunct = new char[] { '(', ')', '*', '-', '.', '!', '_' };

            return ((c >= 'a' && c <= 'z') ||

                    (c >= 'A' && c <= 'Z') ||

                    (c >= '0' && c <= '9') ||

                    safePunct.Contains(c));

        }

    }

}