CompControl.SapFrameworkConnector/CompControl.SapFrameworkConnector/Startup.cs

using Owin;
using System.Web.Http.ExceptionHandling;
using System.Web.Http;
using Microsoft.Owin;
using System.Net.Http;
using System.Net;
using System.Threading.Tasks;
using System.Threading;
using System;

[assembly: OwinStartup(typeof(CompControl.SapFrameworkConnector.Startup))]
[assembly: log4net.Config.XmlConfigurator(ConfigFile = "Log4Net.config", Watch = true)]

namespace CompControl.SapFrameworkConnector
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            HttpConfiguration config = new HttpConfiguration();
            config.Services.Replace(typeof(IExceptionLogger), new UnhandledExceptionLogger());
            config.Services.Replace(typeof(IExceptionHandler), new GlobalExceptionHandler());
            config.MapHttpAttributeRoutes();
            config.Routes.MapHttpRoute(name: "DefaultApi", routeTemplate: "api/{controller}/{id}", defaults: new { id = RouteParameter.Optional });
            app.UseWebApi(config);
        }
    }

    class UnhandledExceptionLogger : ExceptionLogger
    {
        private static readonly log4net.ILog _log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
        public override void Log(ExceptionLoggerContext context) { _log.Error("Web API - Unhandled Exception", context.Exception); }
    }

    class GlobalExceptionHandler : ExceptionHandler
    {
        public override void Handle(ExceptionHandlerContext context)
        {
            if (context.Exception is ArgumentNullException)
            {
                var result = new HttpResponseMessage(HttpStatusCode.BadRequest)
                {
                    Content = new StringContent(context.Exception.Message),
                    ReasonPhrase = "ArgumentNullException"
                };

                context.Result = new ArgumentNullResult(context.Request, result);
            }
            else
            {
                // Handle other exceptions
                context.Result = new TextPlainErrorResult
                {
                    Request = context.ExceptionContext.Request,
                    Content = context.Exception.Message,
                    ReasonPhrase = "Unhandled Web API Exception"
                };
            }
        }

        private class TextPlainErrorResult : IHttpActionResult
        {
            public HttpRequestMessage Request { get; set; }
            public string Content { get; set; }
            public string ReasonPhrase { get; set; }

            public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
            {
                HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.InternalServerError);
                response.Content = new StringContent(Content);
                response.RequestMessage = Request;
                response.ReasonPhrase = ReasonPhrase;
                return Task.FromResult(response);
            }
        }

        private class ArgumentNullResult : IHttpActionResult
        {
            private HttpRequestMessage _request;
            private HttpResponseMessage _httpResponseMessage;


            public ArgumentNullResult(HttpRequestMessage request, HttpResponseMessage httpResponseMessage)
            {
                _request = request;
                _httpResponseMessage = httpResponseMessage;
            }

            public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
            {
                return Task.FromResult(_httpResponseMessage);
            }
        }
    }
}