How to expose a JSON endpoint from a WCF-service

Having seen the small footprint set by JSON – I’ve begun using it extensively for mobile device (WP7) communication. In particular the phone scenario makes it desirable to have an as small as possible data load to transfer between server and device. When using the JSON formatting, you can really minimize the load as documented here. Below is what is returned in JSON-format (compare that to the verbose OData or SOAP formatting!):

[{"BirthYear":1900,"FirstName":"Anders","LastName":"And"},{"BirthYear":1900,"FirstName":"Anders","LastName":"And"},{"BirthYear":1900,"FirstName":"Anders","LastName":"And"},{"BirthYear":1900,"FirstName":"Anders","LastName":"And"},{"BirthYear":1900,"FirstName":"Anders","LastName":"And"}]

How to do ?
To expose a WCF-implemented service with JSON support, you need to setup these artifacts:

Service Contract:
First define the contract for the service to expose.

namespace WebService1
{
    [ServiceContract(Namespace="http://someethingelse.com")]
    public interface IEmployeeService
    {
        [OperationContract]
        [WebInvoke(BodyStyle=WebMessageBodyStyle.Bare, ResponseFormat=WebMessageFormat.Json)]
        Employee[] GetAll_POST();

        [OperationContract]
        [WebGet(BodyStyle = WebMessageBodyStyle.Bare, ResponseFormat = WebMessageFormat.Json)]
        Employee[] GetAll_GET();
    }

    [DataContract(Namespace="http://somethingunique.com")]
    public class Employee
    {
        [DataMember]
        public int BirthYear { get; set; }
        [DataMember]
        public string FirstName { get; set; }
        [DataMember]
        public string LastName { get; set; }
    }
}

Note the WebInvoke and WebGet attributes on the service definition. The WebInvoke attribute specifies that the method will obey POST-requests, where as the WebGet attribute will make the method obey GET-requests.

The two attributes takes parameters that allows for specifying in which format the data should be formatted. When the ResponseFormat=WebMessageFormat.Json is set, the data returned by the method is formatted as a clean and simple JSON notation.

Web.config
Of-course you also need to setup configuration in the web.config. Here you should pay special attention to the binding and the behaviorConfiguration attributes.
Important: In particular the endpointBehavior should have <webHttp> set as content to gain the clean JSON formatting (see below).

  <system.serviceModel>
    <services>
      <service name="WebService1.EmployeeService">
        <endpoint name="jsonEP"
                  address=""
                  binding="webHttpBinding"
                  behaviorConfiguration="json"
                  contract="WebService1.IEmployeeService"/>
      </service>
    </services>
    <behaviors>
      <endpointBehaviors>
        <behavior name="json">
          <webHttp/>
        </behavior>
      </endpointBehaviors>
    </behaviors>
  </system.serviceModel>

Client:
When calling the above service, you will receive a nicely formatted JSON string like this:

[{"BirthYear":1900,"FirstName":"Anders","LastName":"And"},{"BirthYear":1900,"FirstName":"Anders","LastName":"And"},{"BirthYear":1900,"FirstName":"Anders","LastName":"And"},{"BirthYear":1900,"FirstName":"Anders","LastName":"And"},{"BirthYear":1900,"FirstName":"Anders","LastName":"And"}]

That’s how easy it is setting up when using WCF.

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