在 ASP.NET MVC 中设置默认 JSON 序列化程序

Question

我正在处理已部分转换为 MVC 的现有应用程序。每当控制器以 JSON ActionResult 响应时，枚举都作为数字而不是字符串名称发送。听起来默认的序列化程序应该是 JSON.Net，它应该将枚举作为它们的名称发送过来，而不是整数表示，但这里不是这种情况。

我是否缺少将其设置为默认序列化程序的 web.config 设置？还是有其他需要更改的设置？

Answer 1

在 ASP.Net MVC4 中，JsonResult 类中使用的默认 JavaScript 序列化程序仍然是 JavaScriptSerializer（您可以在 code 中查看）

我认为您将它与 ASP.Net Web.API 混淆了，其中 JSON.Net 是默认的 JS 序列化程序，但 MVC4 不使用它。

所以你需要配置 JSON.Net 才能使用 MVC4（基本上你需要创建自己的JsonNetResult），关于它的文章很多：

• ASP.NET MVC and Json.NET
• Using JSON.NET as the default JSON serializer in ASP.NET MVC 3 - is it possible?

如果您还想将 JSON.Net 用于控制器操作参数，那么在模型绑定期间，您需要编写自己的 ValueProviderFactory 实现。

你需要注册你的实现：

ValueProviderFactories.Factories
    .Remove(ValueProviderFactories.Factories
                                  .OfType<JsonValueProviderFactory>().Single());
ValueProviderFactories.Factories.Add(new MyJsonValueProviderFactory());

你可以使用内置的JsonValueProviderFactory作为例子或者这篇文章：ASP.NET MVC 3 – Improved JsonValueProviderFactory using Json.Net

Answer 2

ASP.NET MVC 5 修复：

我还没有准备好更改为 Json.NET，就我而言，错误是在请求期间发生的。在我的场景中，最好的方法是修改实际的JsonValueProviderFactory，它将修复应用于全局项目，并且可以通过编辑global.cs 文件来完成。

JsonValueProviderConfig.Config(ValueProviderFactories.Factories);

添加一个 web.config 条目：

<add key="aspnet:MaxJsonLength" value="20971520" />

然后创建以下两个类

public class JsonValueProviderConfig
{
    public static void Config(ValueProviderFactoryCollection factories)
    {
        var jsonProviderFactory = factories.OfType<JsonValueProviderFactory>().Single();
        factories.Remove(jsonProviderFactory);
        factories.Add(new CustomJsonValueProviderFactory());
    }
}

这基本上是System.Web.Mvc 中的默认实现的精确副本，但添加了可配置的 web.config appsetting 值aspnet:MaxJsonLength。

public class CustomJsonValueProviderFactory : ValueProviderFactory
{

    /// <summary>Returns a JSON value-provider object for the specified controller context.</summary>
    /// <returns>A JSON value-provider object for the specified controller context.</returns>
    /// <param name="controllerContext">The controller context.</param>
    public override IValueProvider GetValueProvider(ControllerContext controllerContext)
    {
        if (controllerContext == null)
            throw new ArgumentNullException("controllerContext");

        object deserializedObject = CustomJsonValueProviderFactory.GetDeserializedObject(controllerContext);
        if (deserializedObject == null)
            return null;

        Dictionary<string, object> strs = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
        CustomJsonValueProviderFactory.AddToBackingStore(new CustomJsonValueProviderFactory.EntryLimitedDictionary(strs), string.Empty, deserializedObject);

        return new DictionaryValueProvider<object>(strs, CultureInfo.CurrentCulture);
    }

    private static object GetDeserializedObject(ControllerContext controllerContext)
    {
        if (!controllerContext.HttpContext.Request.ContentType.StartsWith("application/json", StringComparison.OrdinalIgnoreCase))
            return null;

        string fullStreamString = (new StreamReader(controllerContext.HttpContext.Request.InputStream)).ReadToEnd();
        if (string.IsNullOrEmpty(fullStreamString))
            return null;

        var serializer = new JavaScriptSerializer()
        {
            MaxJsonLength = CustomJsonValueProviderFactory.GetMaxJsonLength()
        };
        return serializer.DeserializeObject(fullStreamString);
    }

    private static void AddToBackingStore(EntryLimitedDictionary backingStore, string prefix, object value)
    {
        IDictionary<string, object> strs = value as IDictionary<string, object>;
        if (strs != null)
        {
            foreach (KeyValuePair<string, object> keyValuePair in strs)
                CustomJsonValueProviderFactory.AddToBackingStore(backingStore, CustomJsonValueProviderFactory.MakePropertyKey(prefix, keyValuePair.Key), keyValuePair.Value);

            return;
        }

        IList lists = value as IList;
        if (lists == null)
        {
            backingStore.Add(prefix, value);
            return;
        }

        for (int i = 0; i < lists.Count; i++)
        {
            CustomJsonValueProviderFactory.AddToBackingStore(backingStore, CustomJsonValueProviderFactory.MakeArrayKey(prefix, i), lists[i]);
        }
    }

    private class EntryLimitedDictionary
    {
        private static int _maximumDepth;

        private readonly IDictionary<string, object> _innerDictionary;

        private int _itemCount;

        static EntryLimitedDictionary()
        {
            _maximumDepth = CustomJsonValueProviderFactory.GetMaximumDepth();
        }

        public EntryLimitedDictionary(IDictionary<string, object> innerDictionary)
        {
            this._innerDictionary = innerDictionary;
        }

        public void Add(string key, object value)
        {
            int num = this._itemCount + 1;
            this._itemCount = num;
            if (num > _maximumDepth)
            {
                throw new InvalidOperationException("The length of the string exceeds the value set on the maxJsonLength property.");
            }
            this._innerDictionary.Add(key, value);
        }
    }

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

    private static string MakePropertyKey(string prefix, string propertyName)
    {
        if (string.IsNullOrEmpty(prefix))
        {
            return propertyName;
        }
        return string.Concat(prefix, ".", propertyName);
    }

    private static int GetMaximumDepth()
    {
        int num;
        NameValueCollection appSettings = ConfigurationManager.AppSettings;
        if (appSettings != null)
        {
            string[] values = appSettings.GetValues("aspnet:MaxJsonDeserializerMembers");
            if (values != null && values.Length != 0 && int.TryParse(values[0], out num))
            {
                return num;
            }
        }
        return 1000;
    }

    private static int GetMaxJsonLength()
    {
        int num;
        NameValueCollection appSettings = ConfigurationManager.AppSettings;
        if (appSettings != null)
        {
            string[] values = appSettings.GetValues("aspnet:MaxJsonLength");
            if (values != null && values.Length != 0 && int.TryParse(values[0], out num))
            {
                return num;
            }
        }
        return 1000;
    }
}