如何从WCF服务返回Json？

using System.ServiceModel.Web;
using System.Runtime.Serialization.Json;

[ServiceContract]
public interface IMyService
{
    [OperationContract]
    [WebGet(ResponseFormat = WebMessageFormat.Json)]
    string GetData();
}

public class MyService : IMyService
{
    public string GetData()
    {
        return "Hello, WCF JSON!";
    }
}

[DataContract]
public class MyData
{
    [DataMember]
    public string Name { get; set; }

    [DataMember]
    public int Age { get; set; }
}

[OperationContract]
[WebGet(ResponseFormat = WebMessageFormat.Json)]
MyData GetData();

public class MyService : IMyService
{
    public MyData GetData()
    {
        return new MyData { Name = "John Doe", Age = 30 };
    }
}

  <behaviors>
   <serviceBehaviors>
      <behavior name="MyServiceBehavior">
       <serviceMetadata httpGetEnabled="true" />
      </behavior>
    </serviceBehaviors>
  </behaviors>
 <services>
   <service name="MyService" behaviorConfiguration="MyServiceBehavior">
     <endpoint address="" binding="webHttpBinding" contract="IMyService" behaviorConfiguration="WebBehavior" />
    </service>
  </services>
  <behaviors>
   <endpointBehaviors>
      <behavior name="WebBehavior">
        <webHttp />
      </behavior>
    </endpointBehaviors>
  </behaviors>
</system.serviceModel>