1 [ArgumentException: 使用 JSON JavaScriptSerializer 序列化或还原序列化期间发生错误。字符串的长度超过在 maxJsonLength 属性上设定的值。 2 参数名称: input] 3 System.Web.Script.Serialization.JavaScriptSerializer.Deserialize(JavaScriptSerializer serializer, String input, Type type, Int32 depthLimit) +168 4 System.Web.Mvc.JsonValueProviderFactory.GetDeserializedObject(ControllerContext controllerContext) +213 5 System.Web.Mvc.JsonValueProviderFactory.GetValueProvider(ControllerContext controllerContext) +16 6 System.Web.Mvc.ValueProviderFactoryCollection.GetValueProvider(ControllerContext controllerContext) +69 7 System.Web.Mvc.ControllerBase.get_ValueProvider() +30
由于前端 Post 到 Action 的参数太大，超过了2M，还没进入后台的 Action 方法就报错了。这个问题困扰了很久，一直未解决。网上找了几个方法都无效。
在 web.config 中加入这些，没有作用：
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<appSettings> <add key="aspnet:MaxJsonDeserializerMembers" value="2147483647" /> <add key="aspnet:UpdatePanelMaxScriptLength" value="2147483647" /></appSettings> |
在 web.config 中加入这些，也没有作用：
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<system.web.extensions> <scripting> <webServices> <jsonSerialization maxJsonLength="2147483647"> </jsonSerialization> </webServices> </scripting></system.web.extensions> |
仔细看了一下异常信息，发现，是在System.Web.Mvc.JsonValueProviderFactory 里调用的 JavaScriptSerializer：
于是查了一下 ，发现 JsonValueProviderFactory 在 System.Web.Mvc.dll 程序集里的：
反编译 System.Web.Mvc.dll 找到 JsonValueProviderFactory 类：
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using System;using System.Collections;using System.Collections.Generic;using System.Collections.Specialized;using System.Configuration;using System.Globalization;using System.IO;using System.Web.Mvc.Properties;using System.Web.Script.Serialization;namespace System.Web.Mvc{ public sealed class JsonValueProviderFactory : ValueProviderFactory { private class EntryLimitedDictionary { private static int _maximumDepth = JsonValueProviderFactory.EntryLimitedDictionary.GetMaximumDepth(); private readonly IDictionary<string, object> _innerDictionary; private int _itemCount; public EntryLimitedDictionary(IDictionary<string, object> innerDictionary) { this._innerDictionary = innerDictionary; } public void Add(string key, object value) { if (++this._itemCount > JsonValueProviderFactory.EntryLimitedDictionary._maximumDepth) { throw new InvalidOperationException(MvcResources.JsonValueProviderFactory_RequestTooLarge); } this._innerDictionary.Add(key, value); } private static int GetMaximumDepth() { NameValueCollection appSettings = ConfigurationManager.AppSettings; if (appSettings != null) { string[] values = appSettings.GetValues("aspnet:MaxJsonDeserializerMembers"); int result; if (values != null && values.Length > 0 && int.TryParse(values[0], out result)) { return result; } } return 1000; } } private static void AddToBackingStore(JsonValueProviderFactory.EntryLimitedDictionary backingStore, string prefix, object value) { IDictionary<string, object> dictionary = value as IDictionary<string, object>; if (dictionary != null) { foreach (KeyValuePair<string, object> current in dictionary) { JsonValueProviderFactory.AddToBackingStore(backingStore, JsonValueProviderFactory.MakePropertyKey(prefix, current.Key), current.Value); } return; } IList list = value as IList; if (list != null) { for (int i = 0; i < list.Count; i++) { JsonValueProviderFactory.AddToBackingStore(backingStore, JsonValueProviderFactory.MakeArrayKey(prefix, i), list[i]); } return; } backingStore.Add(prefix, value); } private static object GetDeserializedObject(ControllerContext controllerContext) { if (!controllerContext.HttpContext.Request.ContentType.StartsWith("application/json", StringComparison.OrdinalIgnoreCase)) { return null; } StreamReader streamReader = new StreamReader(controllerContext.HttpContext.Request.InputStream); string text = streamReader.ReadToEnd(); if (string.IsNullOrEmpty(text)) { return null; } // 问题就出在这里，没有给 javaScriptSerializer.MaxJsonLength 赋值，其默认值是 2097152 字节，即2M JavaScriptSerializer javaScriptSerializer = new JavaScriptSerializer(); return javaScriptSerializer.DeserializeObject(text); } public override IValueProvider GetValueProvider(ControllerContext controllerContext) { if (controllerContext == null) { throw new ArgumentNullException("controllerContext"); } object deserializedObject = JsonValueProviderFactory.GetDeserializedObject(controllerContext); if (deserializedObject == null) { return null; } Dictionary<string, object> dictionary = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase); JsonValueProviderFactory.EntryLimitedDictionary backingStore = new JsonValueProviderFactory.EntryLimitedDictionary(dictionary); JsonValueProviderFactory.AddToBackingStore(backingStore, string.Empty, deserializedObject); return new DictionaryValueProvider<object>(dictionary, CultureInfo.CurrentCulture); } private static string MakeArrayKey(string prefix, int index) { return prefix + "[" + index.ToString(CultureInfo.InvariantCulture) + "]"; } private static string MakePropertyKey(string prefix, string propertyName) { if (!string.IsNullOrEmpty(prefix)) { return prefix + "." + propertyName; } return propertyName; } }} |
在 JavaScriptSerializer 没有设置 MaxJsonLength，默认值是 2097152 字节，即2M。
解决此问题的方法就是 把 javaScriptSerializer.MaxJsonLength = int.MaxValue; （int.MaxValue 值是 2147483647 字节，即2048M）
自己重写类 JsonValueProviderFactory 命名为 MyJsonValueProviderFactory：
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using System;using System.Collections;using System.Collections.Generic;using System.Collections.Specialized;using System.Configuration;using System.Globalization;using System.IO;using System.Web.Mvc;using System.Web.Mvc.Properties;using System.Web.Script.Serialization;namespace XXX{ public sealed class MyJsonValueProviderFactory : ValueProviderFactory { private class EntryLimitedDictionary { private static int _maximumDepth = GetMaximumDepth(); private readonly IDictionary<string, object> _innerDictionary; private int _itemCount; public EntryLimitedDictionary(IDictionary<string, object> innerDictionary) { this._innerDictionary = innerDictionary; } public void Add(string key, object value) { if (++this._itemCount > _maximumDepth) { //throw new InvalidOperationException(MvcResources.JsonValueProviderFactory_RequestTooLarge); throw new InvalidOperationException("itemCount is over maximumDepth"); } this._innerDictionary.Add(key, value); } private static int GetMaximumDepth() { NameValueCollection appSettings = ConfigurationManager.AppSettings; if (appSettings != null) { string[] values = appSettings.GetValues("aspnet:MaxJsonDeserializerMembers"); int result; if (values != null && values.Length > 0 && int.TryParse(values[0], out result)) { return result; } } return 1000; } } private static void AddToBackingStore(EntryLimitedDictionary backingStore, string prefix, object value) { IDictionary<string, object> dictionary = value as IDictionary<string, object>; if (dictionary != null) { foreach (KeyValuePair<string, object> current in dictionary) { AddToBackingStore(backingStore, MakePropertyKey(prefix, current.Key), current.Value); } return; } IList list = value as IList; if (list != null) { for (int i = 0; i < list.Count; i++) { AddToBackingStore(backingStore, MakeArrayKey(prefix, i), list[i]); } return; } backingStore.Add(prefix, value); } private static object GetDeserializedObject(ControllerContext controllerContext) { if (!controllerContext.HttpContext.Request.ContentType.StartsWith("application/json", StringComparison.OrdinalIgnoreCase)) { return null; } StreamReader streamReader = new StreamReader(controllerContext.HttpContext.Request.InputStream); string text = streamReader.ReadToEnd(); if (string.IsNullOrEmpty(text)) { return null; } JavaScriptSerializer javaScriptSerializer = new JavaScriptSerializer(); // 解决这个问题： // 使用 JSON JavaScriptSerializer 序列化或还原序列化期间发生错误。字符串的长度超过在 maxJsonLength 属性上设定的值。 javaScriptSerializer.MaxJsonLength = int.MaxValue; // ---------------------------------------- return javaScriptSerializer.DeserializeObject(text); } public override IValueProvider GetValueProvider(ControllerContext controllerContext) { if (controllerContext == null) { throw new ArgumentNullException("controllerContext"); } object deserializedObject = GetDeserializedObject(controllerContext); if (deserializedObject == null) { return null; } Dictionary<string, object> dictionary = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase); EntryLimitedDictionary backingStore = new EntryLimitedDictionary(dictionary); AddToBackingStore(backingStore, string.Empty, deserializedObject); return new DictionaryValueProvider<object>(dictionary, CultureInfo.CurrentCulture); } private static string MakeArrayKey(string prefix, int index) { return prefix + "[" + index.ToString(CultureInfo.InvariantCulture) + "]"; } private static string MakePropertyKey(string prefix, string propertyName) { if (!string.IsNullOrEmpty(prefix)) { return prefix + "." + propertyName; } return propertyName; } }} |
然后在 Global.asax 中的 Application_Start() 方法里，加入如下代码，用 MyJsonValueProviderFactory 类代替 System.Web.Mvc.dll 程序集中的 JsonValueProviderFactory 类。
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ValueProviderFactories.Factories.Remove(ValueProviderFactories.Factories.OfType<JsonValueProviderFactory>().FirstOrDefault());ValueProviderFactories.Factories.Add(new MyJsonValueProviderFactory()); |
至此，.NET MVC 超出 maxJsonLength 的问题终于解决了！