您可以在web中配置json请求的最大长度。配置文件:

<configuration>
    <system.web.extensions>
        <scripting>
            <webServices>
                <jsonSerialization maxJsonLength="....">
                </jsonSerialization>
            </webServices>
        </scripting>
    </system.web.extensions>
</configuration>

maxJsonLength的缺省值是102400。更多详细信息，请参见MSDN页面:http://msdn.microsoft.com/en-us/library/bb763183.aspx

如果你正在使用MVC 4，一定要看看这个答案。

如果你仍然收到错误:

在web.config中将maxJsonLength属性设置为最大值之后 你知道你的数据长度小于这个值 并且您没有使用web服务方法进行JavaScript序列化

你的问题可能是:

MaxJsonLength属性的值仅应用于异步通信层用于调用Web服务方法的内部JavaScriptSerializer实例。(MSDN: ScriptingJsonSerializationSection。MaxJsonLength属性)

基本上，当从web方法调用时，“内部”JavaScriptSerializer尊重maxJsonLength的值;直接使用JavaScriptSerializer(或通过MVC action-method/Controller使用)不尊重maxJsonLength属性，至少不尊重web.config的systemwebextension .scripting. webservices . jsonserialization部分。特别是，Controller.Json()方法不尊重配置设置!

作为一种变通方法，你可以在你的控制器(或任何地方)中执行以下操作:

var serializer = new JavaScriptSerializer();

// For simplicity just use Int32's max value.
// You could always read the value from the config section mentioned above.
serializer.MaxJsonLength = Int32.MaxValue;

var resultData = new { Value = "foo", Text = "var" };
var result = new ContentResult{
    Content = serializer.Serialize(resultData),
    ContentType = "application/json"
};
return result;

这个答案是我对这个asp.net论坛答案的解释。

使用lib \ Newtonsoft.Json.dll

public string serializeObj(dynamic json) {        
    return JsonConvert.SerializeObject(json);
}

我遵循了vestial的答案，得到了这个解决方案:

当我需要将一个大的json发送到控制器中的一个动作时，我会得到著名的“使用json JavaScriptSerializer进行反序列化期间错误”。字符串的长度超过maxJsonLength属性设置的值。\r\n参数名称:输入值提供程序”。

我所做的是创建一个新的ValueProviderFactory, LargeJsonValueProviderFactory，并设置MaxJsonLength = Int32。GetDeserializedObject方法中的MaxValue

public sealed class LargeJsonValueProviderFactory : ValueProviderFactory
{
private static void AddToBackingStore(LargeJsonValueProviderFactory.EntryLimitedDictionary backingStore, string prefix, object value)
{
    IDictionary<string, object> dictionary = value as IDictionary<string, object>;
    if (dictionary != null)
    {
        foreach (KeyValuePair<string, object> keyValuePair in (IEnumerable<KeyValuePair<string, object>>) dictionary)
            LargeJsonValueProviderFactory.AddToBackingStore(backingStore, LargeJsonValueProviderFactory.MakePropertyKey(prefix, keyValuePair.Key), keyValuePair.Value);
    }
    else
    {
        IList list = value as IList;
        if (list != null)
        {
            for (int index = 0; index < list.Count; ++index)
                LargeJsonValueProviderFactory.AddToBackingStore(backingStore, LargeJsonValueProviderFactory.MakeArrayKey(prefix, index), list[index]);
        }
        else
            backingStore.Add(prefix, value);
    }
}

private static object GetDeserializedObject(ControllerContext controllerContext)
{
    if (!controllerContext.HttpContext.Request.ContentType.StartsWith("application/json", StringComparison.OrdinalIgnoreCase))
        return (object) null;
    string end = new StreamReader(controllerContext.HttpContext.Request.InputStream).ReadToEnd();
    if (string.IsNullOrEmpty(end))
        return (object) null;

    var serializer = new JavaScriptSerializer {MaxJsonLength = Int32.MaxValue};

    return serializer.DeserializeObject(end);
}

/// <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 = LargeJsonValueProviderFactory.GetDeserializedObject(controllerContext);
    if (deserializedObject == null)
        return (IValueProvider) null;
    Dictionary<string, object> dictionary = new Dictionary<string, object>((IEqualityComparer<string>) StringComparer.OrdinalIgnoreCase);
    LargeJsonValueProviderFactory.AddToBackingStore(new LargeJsonValueProviderFactory.EntryLimitedDictionary((IDictionary<string, object>) dictionary), string.Empty, deserializedObject);
    return (IValueProvider) new DictionaryValueProvider<object>((IDictionary<string, object>) dictionary, CultureInfo.CurrentCulture);
}

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

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

private class EntryLimitedDictionary
{
    private static int _maximumDepth = LargeJsonValueProviderFactory.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 > LargeJsonValueProviderFactory.EntryLimitedDictionary._maximumDepth)
            throw new InvalidOperationException("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;
     }
  }
}

然后，在Global.asax.cs中的Application_Start方法中，用新的ValueProviderFactory替换ValueProviderFactory:

protected void Application_Start()
{
    ...

    //Add LargeJsonValueProviderFactory
    ValueProviderFactory jsonFactory = null;
    foreach (var factory in ValueProviderFactories.Factories)
    {
        if (factory.GetType().FullName == "System.Web.Mvc.JsonValueProviderFactory")
        {
            jsonFactory = factory;
            break;
        }
    }

    if (jsonFactory != null)
    {
        ValueProviderFactories.Factories.Remove(jsonFactory);
    }

    var largeJsonValueProviderFactory = new LargeJsonValueProviderFactory();
    ValueProviderFactories.Factories.Add(largeJsonValueProviderFactory);
}

我建议设置为Int32.MaxValue。

JavaScriptSerializer serializer = new JavaScriptSerializer();
serializer.MaxJsonLength = Int32.MaxValue;

注意:这个答案只适用于Web服务，如果你从Controller方法返回JSON，请确保你也阅读了下面的SO答案:https://stackoverflow.com/a/7207539/1246870

MaxJsonLength属性不能无限制，是一个默认为102400 (100k)的整数属性。

你可以在你的web.config中设置MaxJsonLength属性:

<configuration> 
   <system.web.extensions>
       <scripting>
           <webServices>
               <jsonSerialization maxJsonLength="50000000"/>
           </webServices>
       </scripting>
   </system.web.extensions>
</configuration>