使用JSON.Net（Newtonsoft.Json）作为ASP.Net MVC的json序列化和反序列化工具

ASP.Net MVC默认的JSON序列化使用的是微软自己的JavaScriptSerializer。性能低不说，最让人受不了的是Dictionary<,>和Hashtable类型居然对应的json是[{"Key":"a","Value":1}]而不是{"a":1}。真是奇葩到家了，跟前端根本没法集成！

决定还是用JSON.Net来做吧！查了各种资料，网上的要么代码太复杂，要么没法完全实现。又在ILSpy分析了MVC源码，然后调试了半天，终于有了初步的解决办法：

1、反序列化，首先建立下面的类：

原理基本上就是替换系统自带的ValueProviderFactory和DefaultModelBinder，然后改用自己的类来调用JSON.Net实现。

public class JsonNetValueProviderFactory : ValueProviderFactory
    {
        public override IValueProvider GetValueProvider(ControllerContext ctlContext)
        {
            //if (!controllerContext.HttpContext.Request.ContentType.
            //    StartsWith("application/json", StringComparison.OrdinalIgnoreCase))
            //{
            //    return null;
            //}

            var reader = new StreamReader(ctlContext.HttpContext.Request.InputStream);
            reader.BaseStream.Position = 0;
            var json = reader.ReadToEnd()?.TrimStart(' ', '
', '
', '	');
            if (string.IsNullOrEmpty(json))
                return null;

            var jtoken = json.StartsWith("[")
                ? JArray.Parse(json) as JContainer
                : JObject.Parse(json) as JContainer;
            return new JsonNetValueProvider(jtoken);
        }
    }

    public class JsonNetValueProvider : IValueProvider
    {
        private JContainer _jValue;

        public JsonNetValueProvider(JContainer jval)
        {
            _jValue = jval;
        }

        public bool ContainsPrefix(string prefix)
        {
            return true;
        }

        public ValueProviderResult GetValue(string key)
        {
            var jtoken = _jValue.SelectToken(key);
            if (jtoken == null)
            {
                jtoken = _jValue;
            }
            return new JsonNetValueProviderResult(jtoken, key, null);
        }
    }

    public class JsonNetValueProviderResult : ValueProviderResult
    {
        private JToken _jtoken;
        public JsonNetValueProviderResult(JToken valueRaw, string key, CultureInfo info)
        {
            _jtoken = valueRaw;
        }
        [System.Diagnostics.DebuggerHidden]
        public override object ConvertTo(Type type, CultureInfo culture)
        {
            return _jtoken?.ToObject(type);
        }
    }

    public class JsonNetModelBinder : DefaultModelBinder
    {
        [System.Diagnostics.DebuggerHidden]
        public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            var provider = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
            if (provider != null)
            {
                try
                {
                    return provider.ConvertTo(bindingContext.ModelType);
                }
                catch { }
            }
            return base.BindModel(controllerContext, bindingContext);
        }
    }

2、然后再Application_Start或者Router初始化时调用下面代码：

            //重置Json序列化方式，改用JSON.Net
            ValueProviderFactories.Factories.Remove(ValueProviderFactories.Factories.
                OfType<JsonValueProviderFactory>().FirstOrDefault());
            ValueProviderFactories.Factories.Add(new JsonNetValueProviderFactory());

            //重置系统的Binder，使Dictionary可以正常json
            ModelBinders.Binders.DefaultBinder = new JsonNetModelBinder();

3、序列化的过程比较简单，建立一个JsonNetResult类，然后mvc方法返回这个类型就可以了。

 public class JsonNetResult : JsonResult
    {
        public JsonSerializerSettings Settings { get; private set; }
        public override void ExecuteResult(ControllerContext context)
        {
            //if (context == null)
            //    throw new ArgumentNullException("context");
            //if (this.JsonRequestBehavior == JsonRequestBehavior.DenyGet && string.Equals(context.HttpContext.Request.HttpMethod, "GET", StringComparison.OrdinalIgnoreCase))
            //    throw new InvalidOperationException("JSON GET is not allowed");

            HttpResponseBase response = context.HttpContext.Response;
            response.ContentType = string.IsNullOrEmpty(this.ContentType) ? "application/json" : this.ContentType;

            if (this.ContentEncoding != null)
                response.ContentEncoding = this.ContentEncoding;
            if (this.Data == null)
                return;

            var scriptSerializer = JsonSerializer.Create(this.Settings);

            using (var sw = new StringWriter())
            {
                scriptSerializer.Serialize(sw, this.Data);
                response.Write(sw.ToString());
            }
        }
    }