Create Exception Filter to Handle Unhandled Exceptions in C# ASP.NET WebAPI

An exception filter is executed when a controller method throws any unhandled exception that is not an HttpResponseException exception. The HttpResponseException type is a special case, because it is designed specifically for returning an HTTP response.

Exception filters implement the System.Web.Http.Filters.IExceptionFilter interface. The simplest way to write an exception filter is to derive from the System.Web.Http.Filters.ExceptionFilterAttribute class and override the OnException method.

Below is a filter that converts NotFiniteNumberException exceptions into HTTP status code 416, Requested Range Not Satisfiable.

ExceptionFilterAttribute −

Example

using System;
using System.Net;
using System.Net.Http;
using System.Web.Http.Filters;
namespace DemoWebApplication.Controllers{
   public class ExceptionAttribute : ExceptionFilterAttribute{
      public override void OnException(HttpActionExecutedContext context){
         if (context.Exception is NotFiniteNumberException){
            context.Response = new HttpResponseMessage(HttpStatusCode.RequestedRangeNotSatisfiable);
         }
      }
   }
}

Controller ActionMethod −

Example

using DemoWebApplication.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.Http;
namespace DemoWebApplication.Controllers{
   [Exception]
   public class StudentController : ApiController{
      List<Student> students = new List<Student>{
         new Student{
            Id = 1,
            Name = "Mark"
         },
         new Student{
            Id = 2,
            Name = "John"
         }
      };
      public Student Get(int id){
         if(id <= 0){
            throw new NotFiniteNumberException("The Id is not valid");
         }
         var studentForId = students.FirstOrDefault(x => x.Id == id);
         return studentForId;
      }
   }
}

So let us test the above ExceptionAttribute by passing id = 0 for the controller action method.

The ExceptionAttribute can be registered by any of te following approaches.

• Decorate Action with exception filter.

[Exception]
   public IHttpActionResult Get(int id){
   Return Ok();
}

• Decorate Controller with exception filter.

[Exception]
public class StudentController : ApiController{
   public IHttpActionResult Get(int id){
      Return Ok();
   }
}

• Register exception globally in WebApiConfig.cs.

public static class WebApiConfig{
   public static void Register(HttpConfiguration config){
      config.Filters.Add(new ExceptionAttribute());
   }
}