ASP.NET WebApi自訂回傳訊息Demo

01.ApiResponseSample_Normal.js

{
  "StatusCode": 200,
  "Result": {
    Name = "Wellwind",
    Age = 30
  },
  "Error": null
}

02.ApiResponseSample_Error.js

{
  "StatusCode": 404,
  "Result": null,
  "Error": {
    "ErrorId": "api_doesnt_exist",
    "Message": "此Api不存在"
  }
}

03.ApiResponse.cs

public class ApiResponse
{
    public HttpStatusCode StatusCode { get; set; }

    public object Result { get; set; }

    public object Error { get; set; }
}

04.ApiException.cs

public class ApiException : Exception
{
    public string ErrorId { get; set; }

    public HttpStatusCode StatusCode { get; set; }

    public ApiException()
        : this("API呼叫錯誤")
    {
    }

    public ApiException(string errorMessage)
        : base(errorMessage)
    {
        ErrorId = "unknown_api_error";
        StatusCode = HttpStatusCode.BadRequest;
    }
}

05.ApiDoesntExistException.cs

public class ApiDoesntExistException : ApiException
{
    public ApiDoesntExistException()
        : base("此Api不存在")
    {
        ErrorId = "api_doesnt_exist";
        StatusCode = HttpStatusCode.NotFound;
    }
}

06.ApiResponseAttribute.cs

public class ApiResponseAttribute : ActionFilterAttribute
{
    public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
    {
        base.OnActionExecuted(actionExecutedContext);

        if (actionExecutedContext.Exception != null)
        {
            return;
        }

        var result = new ApiResponse
        {
            StatusCode = actionExecutedContext.ActionContext.Response.StatusCode,
            Result = actionExecutedContext.ActionContext.Response.Content.ReadAsAsync().Result }; 
            // 重新封裝回傳格式
            actionExecutedContext.Response = actionExecutedContext.Request.CreateResponse(result.StatusCode, result); 
        }
    }
}

07.WebApiConfig.cs

// add this line to enable custom api response message
config.Filters.Add(new ApiResponseAttribute());

08.ApiExceptionResponseAttribute.cs

    public class ApiExceptionResponseAttribute : ExceptionFilterAttribute
    {
        /// <param name="actionExecutedContext">動作的內容。</param>
        public override void OnException(System.Web.Http.Filters.HttpActionExecutedContext actionExecutedContext)
        {
            base.OnException(actionExecutedContext);

            // 將錯誤訊息轉成要回傳的ApiResponseResult
            var errorApiResponseResult = exceptionToApiResponse(actionExecutedContext.Exception);

            // 重新打包回傳的訊息
            actionExecutedContext.Response =
                actionExecutedContext.Request.CreateResponse(errorApiResponseResult.StatusCode, errorApiResponseResult);
        }

        private static ApiResponse exceptionToApiResponse(Exception exception)
        {
            var errorApiResponseResult = new ApiResponse();

            if (exception is ApiException)
            {
                var apiException = exception as ApiException;
                errorApiResponseResult.StatusCode = apiException.StatusCode;
                errorApiResponseResult.Error = new
                {
                    ErrorId = apiException.ErrorId,
                    Message = apiException.Message
                };
            }
            else
            {
                errorApiResponseResult.StatusCode = HttpStatusCode.BadRequest;
                errorApiResponseResult.Error = new
                {
                    ErrorId = "",
                    Message = exception.Message
                };
            }
            return errorApiResponseResult;
        }
    }

09.WebApiConfig.cs

// add this line to enable custom api response message when exception thrown
config.Filters.Add(new ApiExceptionResponseAttribute());

10.ExceptionTestController.cs

    public class ExceptionTestController : ApiController
    {
        public object Get()
        {
            throw new Exception("Test Exception Message...");
        }

        public object Post()
        {
            throw new ApiException("Test Api Exception Message...");
        }
    }

11.Global.asax.cs

    public class WebApiApplication : System.Web.HttpApplication
    {
        protected void Application_BeginRequest()
        {
            throw new Exception("thrown by Application_BeginRequest");
        }

        protected void Application_Error()
        {
            var exception = Server.GetLastError();
            if (exception == null)
            {
                return;
            }

            object exceptionToSerialize = exception.InnerException ?? exception;
            Response.ContentType = "text/json";
            Response.Write(
                JsonConvert.SerializeObject(
                    ExceptionUtils.ConvertToApiResponse((Exception)exceptionToSerialize)));
            Response.End();
        }
    }

12.HttpNotFoundAwareDefaultHttpControllerSelector.cs

    /// <summary>
    /// HttpNotFound使用自訂Controller的ApiActionSelector
    /// </summary>
    public class HttpNotFoundAwareControllerActionSelector : ApiControllerActionSelector
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="HttpNotFoundAwareControllerActionSelector"/> class.
        /// </summary>
        public HttpNotFoundAwareControllerActionSelector()
        {
        }

        /// <summary>
        /// 為 <see cref="T:System.Web.Http.Controllers.ApiControllerActionSelector" /> 選取動作。
        /// </summary>
        /// <param name="controllerContext">控制器內容。</param>
        /// <returns>
        /// 選取的動作。
        /// </returns>
        public override HttpActionDescriptor SelectAction(HttpControllerContext controllerContext)
        {
            HttpActionDescriptor decriptor = null;
            try
            {
                decriptor = base.SelectAction(controllerContext);
            }
            catch (HttpResponseException ex)
            {
                setErrorController(controllerContext, ex);
                decriptor = base.SelectAction(controllerContext);
            }
            return decriptor;
        }

        private static void setErrorController(HttpControllerContext controllerContext, HttpResponseException ex)
        {
            var controllerName = "Error404";
            var code = ex.Response.StatusCode;
            var routeValues = controllerContext.RouteData.Values;
            if (code != HttpStatusCode.NotFound && code != HttpStatusCode.MethodNotAllowed)
            {
                controllerName = "ErrorOthers";
                routeValues["id"] = code;
            }
            routeValues["action"] = "Get";
            controllerContext.Request.Method = HttpMethod.Get;

            IHttpController httpController = new Error404Controller();
            controllerContext.Controller = httpController;
            controllerContext.ControllerDescriptor = new HttpControllerDescriptor(controllerContext.Configuration,
                controllerName, httpController.GetType());
        }
    }

13.HttpNotFoundAwareControllerActionSelector.cs

    /// <summary>
    /// HttpNotFound使用自訂Controller的ControllerSelector
    /// </summary>
    public class HttpNotFoundAwareDefaultHttpControllerSelector : DefaultHttpControllerSelector
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="HttpNotFoundAwareDefaultHttpControllerSelector"/> class.
        /// </summary>
        /// <param name="configuration">設定。</param>
        public HttpNotFoundAwareDefaultHttpControllerSelector(HttpConfiguration configuration)
            : base(configuration)
        {
        }

        /// <summary>
        /// 為指定的 <see cref="T:System.Net.Http.HttpRequestMessage" /> 選取 <see cref="T:System.Web.Http.Controllers.HttpControllerDescriptor" />。
        /// </summary>
        /// <param name="request">HTTP 要求的訊息。</param>
        /// <returns>
        /// 指定之 <see cref="T:System.Net.Http.HttpRequestMessage" /> 適用的 <see cref="T:System.Web.Http.Controllers.HttpControllerDescriptor" /> 執行個體。
        /// </returns>
        public override HttpControllerDescriptor SelectController(HttpRequestMessage request)
        {
            HttpControllerDescriptor decriptor = null;
            try
            {
                decriptor = base.SelectController(request);
            }
            catch (HttpResponseException ex)
            {
                setErrorController(request, ex);

                decriptor = base.SelectController(request);
            }
            return decriptor;
        }

        private static void setErrorController(HttpRequestMessage request, HttpResponseException ex)
        {
            var code = ex.Response.StatusCode;
            var routeValues = request.GetRouteData().Values;
            routeValues["controller"] = "Error";
            if (code == HttpStatusCode.NotFound)
            {
                routeValues["controller"] = "Error404";
            }
            else
            {
                routeValues["controller"] = "ErrorOthers";
                routeValues["id"] = code;
            }
            routeValues["action"] = "Get";
            request.Method = HttpMethod.Get;
        }
    }

14.Error404Controller.cs

    public class Error404Controller : ApiController
    {
        public object Get()
        {
            throw new Exception("找不到此API");
        }
    }

15.ErrorOthersController.cs

    public class ErrorOthersController : ApiController
    {
        public object Get(int id)
        {
            return new HttpStatusCodeResult(id);
        }
    }

16.WebApiConfig.cs

            config.Services.Replace(typeof(IHttpControllerSelector), new HttpNotFoundAwareDefaultHttpControllerSelector(config));
            config.Services.Replace(typeof(IHttpActionSelector), new HttpNotFoundAwareControllerActionSelector());