using System;

using System.Collections.Generic;

using System.Linq;

using System.Reflection;

using Newtonsoft.Json;

using Newtonsoft.Json.Serialization;

public class Program

{

    public static void Main()

    {

        Foo foo = new Foo

        {

            Name = "<b>Foo Bar</b>",

            Description = @"<p class=""intro"">Bada Boom Bada Bing</p>"

        };

        var settings = new JsonSerializerSettings

        {

            ContractResolver = new CustomResolver(),

            Formatting = Formatting.Indented

        };

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

        Console.WriteLine(json);

    }

}

​

​

class Foo

{

    public string Name { get; set; }

    public string Description { get; set; }

}

​

​

public class CustomResolver : DefaultContractResolver

{

    protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)

    {

        IList<JsonProperty> props = base.CreateProperties(type, memberSerialization);

        // Attach an HtmlEncodingValueProvider instance to all string properties

        foreach (JsonProperty prop in props.Where(p => p.PropertyType == typeof(string)))

        {

            PropertyInfo pi = type.GetProperty(prop.UnderlyingName);

            if (pi != null)

            {

                prop.ValueProvider = new HtmlEncodingValueProvider(pi);

            }

        }

        return props;

    }

    protected class HtmlEncodingValueProvider : IValueProvider

    {

        PropertyInfo targetProperty;

        public HtmlEncodingValueProvider(PropertyInfo targetProperty)

        {

            this.targetProperty = targetProperty;

        }

        // SetValue gets called by Json.Net during deserialization.

        // The value parameter has the original value read from the JSON;

        // target is the object on which to set the value.

        public void SetValue(object target, object value)

        {

            targetProperty.SetValue(target, (string)value);

        }

        // GetValue is called by Json.Net during serialization.

        // The target parameter has the object from which to read the string;

        // the return value is the string that gets written to the JSON

        public object GetValue(object target)

        {

            string value = (string)targetProperty.GetValue(target);

            return HttpUtility.HtmlEncode(value);

        }

    }

}

​

​

​

// Note: Following is a stand-in for the System.Web.HttpUtility class,

// as dotnetfiddle apparently does not provide access to the System.Web namespace.

// In your production code, please use the real version provided by .NET; do NOT use this stand-in class.

public static class HttpUtility

{

    public static string HtmlEncode(string s)

    {

        if (s != null)

        {

            // \u0026 is an ampersand; needed here to get around a dotnetfiddle bug

            s = s.Replace("\u0026", "\u0026amp;")

                 .Replace("<", "\u0026lt;")

                 .Replace(">", "\u0026gt;")

                 .Replace("\"", "\u0026quot;");

        }

        return s;

    }

}

​