在MVC中使用Json.Net序列化和反序列化Json对象

在.Net的MVC开发中，经常会使用到Json对象，于是，系统提供了JsonResult这个对象，其本质是调用.Net系统自带的Json序列化类JavaScriptSerializer对数据对象进行序列化。但是这个系统自带的Json序列化对象方法没有Json.Net好用，于是打算有些时候用Json.Net替代默认的实现。

要实现有时候用Json.Net，有时候用默认实现，那么就要保证系统中两种实现并存。对于Server将对象序列化成Json传给Client很简单，我们只需要建立一个新的ActionResult，我们命名为JsonNetResult，然后在Get时，return这个JsonNetResult即可。JsonNetResult的代码实现为：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace MvcJsonNet
{
    using System.IO;
    using System.Web;
    using System.Web.Mvc;
    using Newtonsoft.Json;

    public class JsonNetResult : JsonResult
    {
        public JsonNetResult()
        {
            Settings = new JsonSerializerSettings
            {
                ReferenceLoopHandling = ReferenceLoopHandling.Error
            };
        }
        public JsonNetResult(object data, JsonRequestBehavior behavior = JsonRequestBehavior.AllowGet, string contentType=null, Encoding contentEncoding=null)
        {
            this.Data = data;
            this.JsonRequestBehavior = behavior;
            this.ContentEncoding = contentEncoding;
            this.ContentType = contentType;
        }

        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());
            }
        }
    }
}

要返回一个Json.Net序号列后的对象，那么调用方法是：

[HttpGet]
public ActionResult GetJsonNet()
{
    var myClass = InitClass();
    return new JsonNetResult(myClass);
}

这是Get方法，但是对于ClientPost一个Json回Server，那么就比较麻烦了，需要修改好几处地方：

1，建立Json.Net的ValueProviderFactory，这个类主要就是用于Json字符串的反序列化。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace MvcJsonNet
{
    using System.Collections;
    using System.Dynamic;
    using System.Globalization;
    using System.IO;
    using System.Web.Mvc;
    using System.Web.Script.Serialization;
    using Newtonsoft.Json;

    public class JsonNetValueProviderFactory : ValueProviderFactory
    {
        private void AddToBackingStore(Dictionary<string, object> backingStore, string prefix, object value)
        {
            IDictionary<string, object> d = value as IDictionary<string, object>;
            if (d != null)
            {
                foreach (KeyValuePair<string, object> entry in d)
                {
                    AddToBackingStore(backingStore, MakePropertyKey(prefix, entry.Key), entry.Value);
                }
                return;
            }

            IList l = value as IList;
            if (l != null)
            {
                for (int i = 0; i < l.Count; i++)
                {
                    AddToBackingStore(backingStore, MakeArrayKey(prefix, i), l[i]);
                }
                return;
            }

            // primitive
            backingStore[prefix] = value;
        }

        private object GetDeserializedObject(ControllerContext controllerContext)
        {
            if (!controllerContext.HttpContext.Request.ContentType.StartsWith("application/json", StringComparison.InvariantCultureIgnoreCase))
            {
                // not JSON request
                return null;
            }

            StreamReader reader = new StreamReader(controllerContext.HttpContext.Request.InputStream);
            string bodyText = reader.ReadToEnd();
            if (String.IsNullOrEmpty(bodyText))
            {
                // no JSON data
                return null;
            }
            //接下来的代码是关键，判断content type，如果是json.net，那么就使用Json.Net的反序列化方法，如果不是，那么就使用系统默认的反序列化方法
            if (controllerContext.HttpContext.Request.ContentType.StartsWith("application/json.net", StringComparison.InvariantCultureIgnoreCase))
            {
                var jsonData = JsonConvert.DeserializeObject<ExpandoObject>(bodyText);
                return jsonData;
            }
            else
            {
                JavaScriptSerializer serializer = new JavaScriptSerializer();
                object jsonData = serializer.DeserializeObject(bodyText);
                return jsonData;
            }
        }

        public override IValueProvider GetValueProvider(ControllerContext controllerContext)
        {
            if (controllerContext == null)
            {
                throw new ArgumentNullException("controllerContext");
            }

            object jsonData = GetDeserializedObject(controllerContext);
            if (jsonData == null)
            {
                return null;
            }

            Dictionary<string, object> backingStore = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
            AddToBackingStore(backingStore, String.Empty, jsonData);
            return new DictionaryValueProvider<object>(backingStore, CultureInfo.CurrentCulture);
        }

        private  string MakeArrayKey(string prefix, int index)
        {
            return prefix + "[" + index.ToString(CultureInfo.InvariantCulture) + "]";
        }

        private  string MakePropertyKey(string prefix, string propertyName)
        {
            return (String.IsNullOrEmpty(prefix)) ? propertyName : prefix + "." + propertyName;
        }
    }
}

2，在初始化MVC时替换掉默认的JsonValueProviderFactory。
在Global.asax的Application_Start时，写入以下代码：

ValueProviderFactories.Factories.Remove(ValueProviderFactories.Factories.OfType<JsonValueProviderFactory>().FirstOrDefault());
ValueProviderFactories.Factories.Add(new JsonNetValueProviderFactory());

3，建立新的ModelBinder，命名为JsonNetModelBinder。

namespace MvcJsonNet
{
    using System;
    using System.ComponentModel;
    using System.Diagnostics;
    using System.Globalization;
    using System.Linq;
    using System.Web.Mvc;
    using Newtonsoft.Json;

    public class JsonNetModelBinder : DefaultModelBinder
    {
        protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext,
                                             PropertyDescriptor propertyDescriptor)
        {
            Debug.WriteLine("BindProperty");
            if (!controllerContext.HttpContext.Request.ContentType.StartsWith("application/json.net",
                                                                              StringComparison
                                                                                  .InvariantCultureIgnoreCase))
            {
                //根据Content type来判断，只有json.net这种content type的才会使用该ModelBinder，否则使用默认的Binder
                base.BindProperty(controllerContext, bindingContext, propertyDescriptor);
                return;
            }

            // need to skip properties that aren't part of the request, else we might hit a StackOverflowException
            string name = propertyDescriptor.Name;
            foreach (object attribute in propertyDescriptor.Attributes)
            {
                if (attribute is JsonPropertyAttribute)
                {
                    var jp = attribute as JsonPropertyAttribute;
                    name = jp.PropertyName;
                }
            }

            string fullPropertyKey = CreateSubPropertyName(bindingContext.ModelName, name);
            if (!bindingContext.ValueProvider.ContainsPrefix(fullPropertyKey))
            {
                return;
            }

            // call into the property's model binder
            IModelBinder propertyBinder = Binders.GetBinder(propertyDescriptor.PropertyType);
            object originalPropertyValue = propertyDescriptor.GetValue(bindingContext.Model);
            ModelMetadata propertyMetadata = bindingContext.PropertyMetadata[propertyDescriptor.Name];
            propertyMetadata.Model = originalPropertyValue;
            var innerBindingContext = new ModelBindingContext
                {
                    ModelMetadata = propertyMetadata,
                    ModelName = fullPropertyKey,
                    ModelState = bindingContext.ModelState,
                    ValueProvider = bindingContext.ValueProvider
                };
            object newPropertyValue = GetPropertyValue(controllerContext, innerBindingContext, propertyDescriptor,
                                                       propertyBinder);
            propertyMetadata.Model = newPropertyValue;

            // validation
            ModelState modelState = bindingContext.ModelState[fullPropertyKey];
            if (modelState == null || modelState.Errors.Count == 0)
            {
                if (OnPropertyValidating(controllerContext, bindingContext, propertyDescriptor, newPropertyValue))
                {
                    SetProperty(controllerContext, bindingContext, propertyDescriptor, newPropertyValue);
                    OnPropertyValidated(controllerContext, bindingContext, propertyDescriptor, newPropertyValue);
                }
            }
            else
            {
                SetProperty(controllerContext, bindingContext, propertyDescriptor, newPropertyValue);

                // Convert FormatExceptions (type conversion failures) into InvalidValue messages
                foreach (
                    ModelError error in
                        modelState.Errors.Where(err => String.IsNullOrEmpty(err.ErrorMessage) && err.Exception != null)
                                  .ToList())
                {
                    for (Exception exception = error.Exception; exception != null; exception = exception.InnerException)
                    {
                        if (exception is FormatException)
                        {
                            string displayName = propertyMetadata.GetDisplayName();
                            string errorMessageTemplate = "The value '{0}' is not valid for {1}.";
                            string errorMessage = String.Format(CultureInfo.CurrentCulture, errorMessageTemplate,
                                                                modelState.Value.AttemptedValue, displayName);
                            modelState.Errors.Remove(error);
                            modelState.Errors.Add(errorMessage);
                            break;
                        }
                    }
                }
            }
        }
    }
}

4，建立一个VModel的基类，为该基类添加Attribute，然后在Global中添加Model和Binder的映射。

[ModelBinder(typeof (JsonNetModelBinder))]
public abstract class VEntity
{
    public virtual long Id { get; set; }
}

Global.asax中Application_Start添加代码：

 ModelBinders.Binders.Add(typeof(VEntity), new JsonNetModelBinder());

5在前端Post Json时，指定content type为application/json.net

 function PostJsonNet() {
             var jsonstr = $("#jsonstring")[0].innerHTML;
             $.ajax({
                 url: "MyTest/CreateFromJsonNet",
                 type: "POST",
                 data: jsonstr,
                 contentType: "application/json.net",
                 dataType: "json",
                 success: function (data) {
                     alert(data);

                 }
             });
         }

我们这样处理后，Client在往Server传送Json数据时，如果指定了contentType是application/json，那么就使用系统默认的方法来反序列化对象，如果是application/json.net，那么就使用Json.Net来反序列化。

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