asmx web service returning xml instead of json in .net 4.0

Question

i have just upgraded a test copy of my site to asp.net 4.0 and have noticed a strange issue that only arises when i upload the site to my server.

the site has an asmx web service that returns json, yet when i run the site on my server it returns xml. it as been working fine in asp.net 3.5 for over a year.

the webMethod is decorated with the correct attributes...

[WebMethod][ScriptMethod(ResponseFormat = ResponseFormat.Json)]
public List<LocationRecentChange> RecentChanges()

and on my local machine it returns json.

yet on the server (Windows 2008 64bit) it returns xml.

you can inspect the response on the test site here...

my test site

using firebug console you will see a 200 OK response and a bunch of XML, and on my local machine the data returned is the JSON i expect.

Here is the javascript that calls the service..

function loadRecentData() {
$.ajax({
    type: "POST",
    url: "service/spots.asmx/RecentChanges",
    data: "{}",
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: loadRecentUpdates,
    failure: function(msg) {
        //alert(msg);
    }
});

}

Any suggestions welcome, this has got me stumped!

Answer 1

well i managed to track it down by reading up about ajax web services requests are handled here...

http://www.asp.net/%28S%28ywiyuluxr3qb2dfva1z5lgeg%29%29/learn/ajax/tutorial-05-cs.aspx

basically a handler from asp.net 3.5 needs to be declared in your web.config handlers section under system.webserver so that it can return a JSON response instead of the default.

here is what you need to add to the web.config...

<add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>

i have my suspicions that this will need replacing with a .net 4.0 version of the same handler, but for now, it works.

Answer 2

Are you sure .NET 4 is installed on your server?

The ScriptHandlerFactory's "type" string in .NET 4 is:

System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"

ASP.NET 4 now includes that in its default web.config at the machine level. So, you shouldn't need any mapping to the ScriptHandlerFactory in your project's web.config, 3.5 or 4.