前不久在做一个项目的时候，我用到了mvc的webapi返回了一个大数据，结果报了500错误，如下图所示：

Server Error in ‘/’ Application.

Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidOperationException: Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property.

Source Error:

Stack Trace:

[InvalidOperationException: Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property.]
   System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj, StringBuilder output, SerializationFormat serializationFormat) +551497
   System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj, SerializationFormat serializationFormat) +74
   System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj) +6
   System.Web.Mvc.JsonResult.ExecuteResult(ControllerContext context) +341
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult) +10
   System.Web.Mvc.<>c__DisplayClass14.<InvokeActionResultWithFilters>b__11() +20
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation) +251
   System.Web.Mvc.<>c__DisplayClass16.<InvokeActionResultWithFilters>b__13() +19
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +178
   System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +314
   System.Web.Mvc.Controller.ExecuteCore() +105
   System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +39
   System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +7
   System.Web.Mvc.<>c__DisplayClass8.<BeginProcessRequest>b__4() +34
   System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +21
   System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +12
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +59
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +44
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +7
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8682542
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

从上面可以看出错误的原因是对象在JavaScriptSerializer序列化的时候超过了默认的最大限制，所以我们需要一个类来重写JsonResult从而允许更大的数据。

using System;
using System.Web.Script.Serialization;

namespace System.Web.Mvc
{
    public class LargeJsonResult : JsonResult
    {
        const string JsonRequest_GetNotAllowed = "This request has been blocked because sensitive information could be disclosed to third party web sites when this is used in a GET request. To allow GET requests, set JsonRequestBehavior to AllowGet.";
        public LargeJsonResult()
        {
            MaxJsonLength = 1024000;
            RecursionLimit = 100;
        }

        public int MaxJsonLength { get; set; }
        public int RecursionLimit { get; set; }

        public override void ExecuteResult( ControllerContext context )
        {
            if( context == null )
            {
                throw new ArgumentNullException( "context" );
            }
            if( JsonRequestBehavior == JsonRequestBehavior.DenyGet &&
                String.Equals( context.HttpContext.Request.HttpMethod, "GET", StringComparison.OrdinalIgnoreCase ) )
            {
                throw new InvalidOperationException( JsonRequest_GetNotAllowed );
            }

            HttpResponseBase response = context.HttpContext.Response;

            if( !String.IsNullOrEmpty( ContentType ) )
            {
                response.ContentType = ContentType;
            }
            else
            {
                response.ContentType = "application/json";
            }
            if( ContentEncoding != null )
            {
                response.ContentEncoding = ContentEncoding;
            }
            if( Data != null )
            {
                JavaScriptSerializer serializer = new JavaScriptSerializer() { MaxJsonLength = MaxJsonLength, RecursionLimit = RecursionLimit };
                response.Write( serializer.Serialize( Data ) );
            }
        }
    }
}

　　你可以在Action里面使用return new LargeJsonResult(){ Data = data }  来替代 return Json(data).
当然你也可以自己控制JavaScriptSerializer的MaxJsonLength：

return new LargeJsonResult() { Data = output, MaxJsonLength = int.MaxValue };

转载自：https://brianreiter.org/2011/01/03/custom-jsonresult-class-for-asp-net-mvc-to-avoid-maxjsonlength-exceeded-exception/