asp.net asmx web service returning xml instead of json

C# Problem Overview

Why does this simple web service refuse to return JSON to the client?

Here is my client code:

        var params = { };
        $.ajax({
            url: "/Services/SessionServices.asmx/HelloWorld",
            type: "POST",
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            timeout: 10000,
            data: JSON.stringify(params),
            success: function (response) {
                console.log(response);
            }
        });

And the service:

namespace myproject.frontend.Services
{
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]
    [ScriptService]
    public class SessionServices : System.Web.Services.WebService
    {
        [WebMethod]
        [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
        public string HelloWorld()
        {
            return "Hello World";
        }
    }
}

web.config:

<configuration>
    <system.web>
        <compilation debug="true" targetFramework="4.0" />
    </system.web>
</configuration>

And the response:

<?xml version="1.0" encoding="utf-8"?>
<string xmlns="http://tempuri.org/">Hello World</string>

No matter what I do, the response always comes back as XML. How do I get the web service to return Json?

EDIT:

Here is the Fiddler HTTP trace:

REQUEST
-------
POST http://myproject.local/Services/SessionServices.asmx/HelloWorld HTTP/1.1
Host: myproject.local
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20100101 Firefox/13.0.1
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Content-Type: application/json; charset=utf-8
X-Requested-With: XMLHttpRequest
Referer: http://myproject.local/Pages/Test.aspx
Content-Length: 2
Cookie: ASP.NET_SessionId=5tvpx1ph1uiie2o1c5wzx0bz
Pragma: no-cache
Cache-Control: no-cache

{}

RESPONSE
-------
HTTP/1.1 200 OK
Cache-Control: private, max-age=0
Content-Type: text/xml; charset=utf-8
Server: Microsoft-IIS/7.5
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Tue, 19 Jun 2012 16:33:40 GMT
Content-Length: 96

<?xml version="1.0" encoding="utf-8"?>
<string xmlns="http://tempuri.org/">Hello World</string>

I have lost count of how many articles I have read now trying to fix this. The instructions are either incomplete or do not solve my issue for some reason. Some of the more relevant ones include (all without success):

Plus several other general articles.

C# Solutions

Solution 1 - C#

Finally figured it out.

The app code is correct as posted. The problem is with the configuration. The correct web.config is:

<configuration>
    <system.web>
        <compilation debug="true" targetFramework="4.0" />
    </system.web>
    <system.webServer>
        <handlers>
            <add name="ScriptHandlerFactory"
                 verb="*" path="*.asmx"
                 type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
                 resourceType="Unspecified" />
        </handlers>
    </system.webServer>
</configuration>

According to the docs, registering the handler should be unnecessary from .NET 4 upwards as it has been moved to the machine.config. For whatever reason, this isn't working for me. But adding the registration to the web.config for my app resolved the problem.

A lot of the articles on this problem instruct to add the handler to the <system.web> section. This does NOT work and causes a whole load of other problems. I tried adding the handler to both sections and this generates a set of other migration errors which completely misdirected my troubleshooting.

In case it helps anyone else, if I had ther same problem again, here is the checklist I would review:

Did you specify type: "POST" in the ajax request?
Did you specify contentType: "application/json; charset=utf-8" in the ajax request?
Did you specify dataType: "json"in the ajax request?
Does your .asmx web service include the [ScriptService] attribute?
Does your web method include the [ScriptMethod(ResponseFormat = ResponseFormat.Json)] attribute? (My code works even without this attribute, but a lot of articles say that it is required)
Have you added the ScriptHandlerFactory to the web.config file in <system.webServer><handlers>?
Have you removed all handlers from the the web.config file in in <system.web><httpHandlers>?

Hope this helps anyone with the same problem. and thanks to posters for suggestions.

Solution 2 - C#

No success with above solution, here how I resolved it.

put this line into your webservice and rather return type just write the string in response context

this.Context.Response.ContentType = "application/json; charset=utf-8";
this.Context.Response.Write(serial.Serialize(city));

Solution 3 - C#

If you want to stay remain with Framework 3.5, you need to make change in code as follows.

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
[ScriptService]
public class WebService : System.Web.Services.WebService
{
    public WebService()
    {
    }

    [WebMethod]
    public void HelloWorld() // It's IMP to keep return type void.
    {
        string strResult = "Hello World";
        object objResultD = new { d = strResult }; // To make result similarly like ASP.Net Web Service in JSON form. You can skip if it's not needed in this form.

        System.Web.Script.Serialization.JavaScriptSerializer ser = new System.Web.Script.Serialization.JavaScriptSerializer();
        string strResponse = ser.Serialize(objResultD);

        string strCallback = Context.Request.QueryString["callback"]; // Get callback method name. e.g. jQuery17019982320107502116_1378635607531
        strResponse = strCallback + "(" + strResponse + ")"; // e.g. jQuery17019982320107502116_1378635607531(....)

        Context.Response.Clear();
        Context.Response.ContentType = "application/json";
        Context.Response.AddHeader("content-length", strResponse.Length.ToString());
        Context.Response.Flush();

        Context.Response.Write(strResponse);
    }
}

Solution 4 - C#

There is much easier way to return a pure string from web service. I call it CROW function (makes it easy to remember).

  [WebMethod]
  public void Test()
    {
        Context.Response.Output.Write("and that's how it's done");    
    }

As you can see, return type is "void", but CROW function will still return the value you want.

Solution 5 - C#

I have a .asmx web service (.NET 4.0) with a method that returns a string. The string is a serialized List like you see in many of the examples. This will return json that is not wrapped in XML. No changes to web.config or need for 3rd party DLLs.

var tmsd = new List<TmsData>();
foreach (DataRow dr in dt.Rows)
{

m_firstname = dr["FirstName"].ToString();
m_lastname = dr["LastName"].ToString();

tmsd.Add(new TmsData() { FirstName = m_firstname, LastName = m_lastname} );

}

var serializer = new System.Web.Script.Serialization.JavaScriptSerializer();
string m_json = serializer.Serialize(tmsd);

return m_json;

The client part that uses the service looks like this:

   $.ajax({
       type: 'POST',
       contentType: "application/json; charset=utf-8",
       dataType: 'json',
       url: 'http://localhost:54253/TmsWebService.asmx/GetTombstoneDataJson',
       data: "{'ObjectNumber':'105.1996'}",
       success: function (data) {
           alert(data.d);
       },
       error: function (a) {
           alert(a.responseText);
       }
   });

Solution 6 - C#

Hope this helps, it appears that you still have to send some JSON object in the request, even if the Method you are calling has no parameters.

var params = {};
return $http({
        method: 'POST',
        async: false,
        url: 'service.asmx/ParameterlessMethod',
        data: JSON.stringify(params),
        contentType: 'application/json; charset=utf-8',
        dataType: 'json'

    }).then(function (response) {
        var robj = JSON.parse(response.data.d);
        return robj;
    });

Solution 7 - C#

For me it works with this code I got from this post:

https://stackoverflow.com/questions/3026934/how-can-i-return-json-from-my-wcf-rest-service-net-4-using-json-net-without

[WebInvoke(UriTemplate = "HelloWorld", Method = "GET"), OperationContract]
public Message HelloWorld()
{
	string jsonResponse = //Get JSON string here
	return WebOperationContext.Current.CreateTextResponse(jsonResponse, "application/json; charset=utf-8", Encoding.UTF8);
}

Solution 8 - C#

I have tried all of the above steps ( even the answer), but i was not successful, my system configuration is Windows Server 2012 R2, IIS 8. The following step solved my problem.

Changed the app pool, that has managed pipeline = classic.

Solution 9 - C#

I know that is really old question but i came to same problem today and I've been searching everywhere to find the answer but with no result. After long research I have found the way to make this work. To return JSON from service you have provide data in request in the correct format, use JSON.stringify() to parse the data before request and don't forget about contentType: "application/json; charset=utf-8", using this should provide expected result.

Solution 10 - C#

response = await client.GetAsync(RequestUrl, HttpCompletionOption.ResponseContentRead);
if (response.IsSuccessStatusCode)
{
	_data = await response.Content.ReadAsStringAsync();
	try
	{
		XmlDocument _doc = new XmlDocument();
		_doc.LoadXml(_data);
		return Request.CreateResponse(HttpStatusCode.OK, JObject.Parse(_doc.InnerText));
	}
	catch (Exception jex)
	{
		return Request.CreateResponse(HttpStatusCode.BadRequest, jex.Message);
	}
}
else
	return Task.FromResult<HttpResponseMessage>(Request.CreateResponse(HttpStatusCode.NotFound)).Result;

Content Type	Original Author	Original Content on Stackoverflow
Question	njr101	View Question on Stackoverflow
Solution 1 - C#	njr101	View Answer on Stackoverflow
Solution 2 - C#	Ajay	View Answer on Stackoverflow
Solution 3 - C#	Kalpesh Desai	View Answer on Stackoverflow
Solution 4 - C#	GabrielJ	View Answer on Stackoverflow
Solution 5 - C#	smoore4	View Answer on Stackoverflow
Solution 6 - C#	Otto	View Answer on Stackoverflow
Solution 7 - C#	j0aqu1n	View Answer on Stackoverflow
Solution 8 - C#	Arindam Nayak	View Answer on Stackoverflow
Solution 9 - C#	Sebastian Siewień	View Answer on Stackoverflow
Solution 10 - C#	Mohamed.Abdo	View Answer on Stackoverflow