Handling errors and exceptions effectively in ASP.NET Core applications is crucial for providing a smooth user experience and maintaining application stability. ASP.NET Core provides various strategies and built-in features to manage errors and exceptions. Here’s an overview of the key strategies:
1. Exception Handling Middleware
ASP.NET Core uses middleware to handle exceptions in a centralized manner. The UseExceptionHandler middleware can be configured to capture unhandled exceptions and redirect the user to an error page.
Example in Startup.cs:
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Home/Error");
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
});
}
In this setup:
UseDeveloperExceptionPage: Provides detailed error information in the development environment.UseExceptionHandler: Redirects to a custom error page in non-development environments.
2. Custom Error Pages
You can create custom error pages to provide user-friendly error messages. For example, you can create a Error action in the HomeController to serve an error page.
Example:
public class HomeController : Controller
{
public IActionResult Error()
{
return View();
}
}
And in the Views/Home/Error.cshtml:
@{
ViewData["Title"] = "Error";
}
<h1 class="text-danger">An error occurred while processing your request.</h1>
3. UseStatusCodePages Middleware
The UseStatusCodePages middleware provides a way to handle status codes (e.g., 404 Not Found) and display custom pages.
Example:
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Home/Error");
app.UseHsts();
}
app.UseStatusCodePagesWithRedirects("/Home/StatusCode?code={0}");
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
});
}
In the HomeController:
public IActionResult StatusCode(int code)
{
ViewData["StatusCode"] = code;
return View();
}
4. Exception Filters
Exception filters are a way to handle exceptions at the controller or action level. They allow you to execute code before and after action methods.
Example:
public class CustomExceptionFilter : IExceptionFilter
{
public void OnException(ExceptionContext context)
{
// Log the exception
context.Result = new RedirectToActionResult("Error", "Home", null);
}
}
public void ConfigureServices(IServiceCollection services)
{
services.AddControllersWithViews(options =>
{
options.Filters.Add<CustomExceptionFilter>();
});
}
5. Logging Exceptions
Proper logging is essential for diagnosing and troubleshooting errors. ASP.NET Core’s logging framework can be used to log exceptions.
Example:
public class HomeController : Controller
{
private readonly ILogger<HomeController> _logger;
public HomeController(ILogger<HomeController> logger)
{
_logger = logger;
}
public IActionResult Index()
{
try
{
// Code that may throw an exception
}
catch (Exception ex)
{
_logger.LogError(ex, "An error occurred in the Index action.");
return RedirectToAction("Error");
}
return View();
}
public IActionResult Error()
{
return View();
}
}
6. Global Exception Handling
For global exception handling, you can configure a middleware to catch all unhandled exceptions.
Example:
public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILogger<Startup> logger)
{
app.Use(async (context, next) =>
{
try
{
await next();
}
catch (Exception ex)
{
logger.LogError(ex, "An unhandled exception occurred.");
context.Response.Redirect("/Home/Error");
}
});
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Home/Error");
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
});
}
7. Exception Handling for API Controllers
For API controllers, use the ProblemDetails response type to provide detailed error information in a structured format.
Example:
[ApiController]
[Route("[controller]")]
public class SampleController : ControllerBase
{
[HttpGet]
public IActionResult Get()
{
try
{
// Code that may throw an exception
}
catch (Exception ex)
{
return Problem(detail: ex.Message, statusCode: 500);
}
return Ok();
}
}
Summary
Handling errors and exceptions in ASP.NET Core involves using middleware, custom error pages, exception filters, and proper logging. These strategies ensure that your application can gracefully handle errors, provide meaningful feedback to users, and allow developers to diagnose and fix issues effectively. By combining these approaches, you can build robust and reliable ASP.NET Core applications.
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