以JSON格式返回Web API响应

Question

I am trying sending a response from the API as a JSON. Currently we are calling other web service multiple times consuming it and send all the responses together as a JSON. The called web service returns response as a JSON. And below is what I am doing

    List<Models.DTO.RootObject> i_response = new List<Models.TO.RootObject>();
    public async Task<IHttpActionResult> Get()
    {
    .....
   foreach (int req_id in reqIdLst)
   { 
     using (var client_request = new HttpClient())
      {
       string request_Uri = BaseURL_iLab;
       Uri uri_request = new Uri(request_Uri);
       client_request.BaseAddress = uri_request;
       client_request.DefaultRequestHeaders.Accept.Clear();
       client_request.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
       client_request.DefaultRequestHeaders.Add("Authorization", "Bearer " + accessToken);

       var request_response = await client_request.GetAsync(uri_request);
       var responsefile = await request_response.Content.ReadAsStringAsync();

        var request_returnDataObj = JsonConvert.DeserializeObject<Models.DTO.RootObject>(responsefile);

         i_response.Add(request_returnDataObj);
     }}
      return Ok(i_response);
  }}

But my above code throws error when debugging as

<Error>
<Message>An error has occurred.</Message>
<ExceptionMessage>
The 'ObjectContent`1' type failed to serialize the response body for content 
type 'application/xml; charset=utf-8'.
</ExceptionMessage>
<ExceptionType>System.InvalidOperationException</ExceptionType>
<StackTrace/>
<InnerException>

I am not sure how to send as a JSON instead of a XML.

Answer 1

Something we did where I work was to create a custom class that extends ExceptionFilterAttribute . Call it something like WebApiExceptionFilterAttribute . Create an override for OnException and set the context.Response appropriately based on the exception. You can also set the HttpStatusCode if the exception indicates a specific result, such as NotFound, Forbidden, or BadRequest, instead of just InternalServerError.

Then, in Global.asax , in Application_Start() , add GlobalConfiguration.Configuration.Filters.Add(new WebApiExceptionFilterAttribute());

Finally, when defining an ApiController , add a [WebApiExceptionFilterAttribute] annotation to the class definition.