Introduction :

In this tutorial we are going to discuss How to handle 404 errors in ASP.NET Core MVC, When a web page is not found and a 404 error is returned by the application, ASP.NET Core MVC presents only a generic browser error page.

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How to handle 404 errors in ASP.NET Core MVC

The following is code in Configure() method of Startup class in Startup.cs file. As you might already know, this Configure() method configures the HTTP request processing pipeline for our asp.net core application.

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");

            }
            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Home}/{action=Index}/{id?}");
            });
        }

Default 404 error page in ASP.NET Core

If we do not have anything configured in this http request processing pipeline to handle 404 errors. So if we navigate invalid URL like https://localhost:44377/home/employee, we see the following default 404 error page. This is because the URL /home/employee does not match any routes in our application.

handle 404 errors in ASP.NET Core MVC

To handle non-success http status codes such as 404 for example, we could use the following 3 built-in asp.net core middleware components.

UseStatusCodePages
UseStatusCodePagesWithRedirects
UseStatusCodePagesWithReExecute

UseStatusCodePages Middleware

This is the least useful status code middleware components. For this reason, we rarely use it in a real world production application. To use it in an application and see what it can do, plug it into the http processing pipeline as shown below.

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseStatusCodePages();
                app.UseHsts();
            }
            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Home}/{action=Index}/{id?}");
            });
        }

With UseStatusCodePages Middleware configured, if we navigate to

https://localhost:44377/home/employee, it returns the following simple text response.

UseStatusCodePagesWithRedirects Middleware

In a production quality application we want to intercept these non-success http status codes and return a custom error view. To achieve this, we can either use UseStatusCodePagesWithRedirects middleware or UseStatusCodePagesWithReExecute middleware.

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseStatusCodePagesWithRedirects("/Error/{0}");
                app.UseHsts();
            }
            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Home}/{action=Index}/{id?}");
            });
        }

With the following line in place, if there is a 404 error, the user is redirected to /Error/404. The placeholder {0}, in “/Error/{0}” will automatically receive the http status code.

In HomeController add ActionMethod  HttpStatusCodeHandler

    public class HomeController : Controller
    {

        [Route("Error/{statusCode}")]
        public IActionResult HttpStatusCodeHandler(int statusCode)
        {
            switch (statusCode)
            {
                case 404:
                    ViewBag.ErrorMessage = "404, Requested resource was not found";
                    break;
            }

            return View("PageNotFound");
        }
    
    }

PageNotFound View :

At this point, if we navigate to https://localhost/Home/employee we see the following custom 404 error view PageNotFound.cshtml as expected.

To use UseStatusCodePagesWithReExecute middleware instead of UseStatusCodePagesWithRedirects middleware

we need to replace UseStatusCodePagesWithRedirects(“/Error/{0}”)  middleware with UseStatusCodePagesWithReExecute(“/Error/{0}”)

When we use UseStatusCodePagesWithReExecute middleware we see below error massage with same page URL

Difference between UseStatusCodePagesWithRedirects vs UseStatusCodePagesWithReExecute middleware

UseStatusCodePagesWithRedirects : By using this middleware if error comes then it redirect to error page

UseStatusCodePagesWithReExecute : By using this middleware if error comes then error page content will display but not redirect to error page as shown in above  two screenshot difference.

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