Exception Handling in ASP.NET Core – Complete Guide

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Exception handling is a core architectural requirement in ASP.NET Core applications.
If exceptions are not handled correctly, they can expose sensitive data, crash APIs, and make production debugging extremely difficult.

ASP.NET Core provides two powerful global mechanisms for handling exceptions:

  • Exception Handling Middleware
  • Exception Filters

In this complete guide, you’ll learn:

  • How exception handling works internally in ASP.NET Core
  • Middleware vs Filters – real differences
  • When to use Middleware, Filters, or both
  • Best practices followed in real-world production applications

🔹 Why Exception Handling Is Important in ASP.NET Core

Poor exception handling can lead to:

  • Application crashes ❌
  • Exposed stack traces ❌
  • Inconsistent API responses ❌
  • Difficult debugging and monitoring ❌

Proper exception handling ensures:

  • Centralized error handling ✅
  • Secure and user-friendly API responses ✅
  • Clean and maintainable architecture ✅
  • Better logging and observability ✅

🔹 What Is Exception Handling Middleware in ASP.NET Core?

Exception Handling Middleware runs early in the ASP.NET Core request pipeline.
It catches any unhandled exception, no matter where it occurs.

✔ What Can Middleware Handle?

  • Controller exceptions
  • Service and repository exceptions
  • Database failures
  • Runtime and system errors
  • Exceptions thrown by filters

🔹 Global Exception Handling Middleware

public class ExceptionMiddleware
{
    private readonly RequestDelegate _next;

    public ExceptionMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        try
        {
            await _next(context);
        }
        catch (Exception ex)
        {
            context.Response.StatusCode = StatusCodes.Status500InternalServerError;
            context.Response.ContentType = "application/json";

            var response = new
            {
                message = "Something went wrong. Please try again later.",
                error = ex.Message
            };

            await context.Response.WriteAsJsonAsync(response);
        }
    }
}

Register Middleware in Program.cs

app.UseMiddleware<ExceptionMiddleware>();

Advantages of Exception Handling Middleware

  • ✅ Catches all unhandled exceptions
  • ✅ Ideal for REST APIs
  • ✅ Perfect for centralized logging & monitoring
  • ✅ Ensures consistent error responses

❌ Limitations of Middleware

  • No access to ModelState
  • No controller or action context
  • Cannot handle MVC-specific validation errors

🔹 What Are Exception Filters in ASP.NET Core?

Exception Filters are part of the MVC execution pipeline.
They run only when an exception occurs inside a controller action.

✔ What Can Exception Filters Access?

  • Controller and action context
  • ModelState
  • Action arguments
  • MVC-specific metadata

Custom Exception Filter – Example

public class GlobalExceptionFilter : IExceptionFilter
{
    public void OnException(ExceptionContext context)
    {
        context.Result = new ObjectResult(new
        {
            message = "An error occurred while processing the request.",
            details = context.Exception.Message
        })
        {
            StatusCode = StatusCodes.Status500InternalServerError
        };

        context.ExceptionHandled = true;
    }
}

🔹 Register Filter Globally

services.AddControllers(options =>
{
    options.Filters.Add<GlobalExceptionFilter>();
});

🔹 Advantages of Exception Filters

  • ✅ Access to MVC context
  • ✅ Ideal for validation & business exceptions
  • ✅ Controller-specific error customization

❌ Limitations of Exception Filters

  • Cannot catch middleware or routing errors
  • Works only inside MVC
  • Not suitable for global logging alone

🔹 Middleware vs Filters – Key Differences

FeatureMiddlewareFilters
Pipeline ScopeEntire applicationMVC only
Catches all exceptions✅ Yes❌ No
Access to ModelState❌ No✅ Yes
Best for APIs✅ Yes⚠️ Limited
Logging & Monitoring✅ Excellent❌ Limited

🔹 Which One Should You Use?

✔ Use Middleware When:

  • Building REST APIs
  • Handling global exceptions
  • Implementing centralized logging
  • Returning consistent error responses

✔ Use Filters When:

  • Handling validation errors
  • Customizing controller responses
  • Managing action-level exceptions

🔹 Best Practice: Use Middleware and Filters Together

Enterprise-grade ASP.NET Core applications follow a layered approach:

  • Middleware → Global exception handling & logging
  • Filters → MVC-specific and validation errors

This ensures maximum coverage and clean architecture.

🔹 Exception Handling Flow in ASP.NET Core

HTTP Request
   ↓
Exception Handling Middleware
   ↓
Routing
   ↓
Authorization
   ↓
Exception Filters
   ↓
Controller Action
   ↓
HTTP Response

🔹 Common Interview Question

Q: Should we use Exception Middleware or Exception Filters?

✔ Middleware → Global exception handling
✔ Filters → MVC-specific handling
✔ Best solution → Use both

❓ 1. What is exception handling in ASP.NET Core?

Exception handling in ASP.NET Core is the process of capturing runtime errors and responding to them in a controlled and secure way.
It prevents application crashes, hides sensitive stack traces, and ensures consistent API responses.

❓ 2. What are the ways to handle exceptions in ASP.NET Core?

ASP.NET Core supports multiple exception-handling approaches:

  • Try-catch blocks (local handling)
  • Exception Handling Middleware (global handling)
  • Exception Filters (MVC-specific handling)
  • Developer Exception Page (development only)

For production systems, middleware + filters is the recommended approach.

❓ 3. What is global exception handling in ASP.NET Core?

Global exception handling means capturing all unhandled exceptions at a single place instead of handling them in every controller or service.
This is typically achieved using Exception Handling Middleware.

❓ 4. Why is Exception Handling Middleware preferred for APIs?

Middleware is preferred because:

  • It catches exceptions from the entire request pipeline
  • It provides consistent HTTP responses
  • It supports centralized logging and monitoring
  • It keeps controllers clean and readable

❓ 5. Can Exception Middleware catch exceptions thrown in filters?

Yes ✅
Middleware can catch exceptions thrown by filters, controllers, and services — as long as the middleware is registered before MVC in the pipeline.

❓ 6. What is the limitation of Exception Filters?

Exception Filters:

  • Work only inside the MVC pipeline
  • Cannot catch routing or middleware-level exceptions
  • Are not suitable for centralized logging alone

That’s why they should not replace middleware.

❓ 7. When should we use Exception Filters?

Exception Filters should be used when:

  • You need access to ModelState
  • You want controller-specific error responses
  • You are handling validation or business rule exceptions

❓ 8. Should we use try-catch blocks inside controllers?

In most cases, NO ❌
Using try-catch in every controller:

  • Duplicates code
  • Makes controllers bulky
  • Breaks separation of concerns

Controllers should rely on global exception handling instead.

❓ 9. What is the difference between UseExceptionHandler and custom middleware?

  • UseExceptionHandler is a built-in middleware provided by ASP.NET Core
  • Custom middleware gives more control over response structure, logging, and error mapping

In real-world projects, custom middleware is preferred.

❓ 10. How do you return consistent error responses in ASP.NET Core?

Consistent error responses are achieved by:

  • Using global exception middleware
  • Returning standard HTTP status codes
  • Avoiding raw exception messages in production
  • Logging detailed errors internally

❓ 11. Can we handle validation errors using middleware?

❌ No.
Validation errors occur inside MVC and should be handled using:

  • Exception Filters
  • ModelState validation
  • Action filters

❓ 12. How does exception handling affect application security?

  • Prevents stack trace exposure
  • Hides internal system details
  • Reduces attack surface
  • Improves compliance and security posture

❓ 13. What happens if exceptions are not handled globally?

Without global exception handling:

  • Application may crash
  • Clients receive inconsistent responses
  • Logs become fragmented
  • Debugging becomes difficult in production

❓ 14. Is it a good practice to log exceptions inside controllers?

❌ No.
Logging should be centralized in:

  • Exception Handling Middleware
  • Dedicated logging services

This keeps controllers focused on business logic.

❓ 15. What is the best exception handling strategy in ASP.NET Core?

✔ Global Exception Handling Middleware
✔ Exception Filters for MVC-specific errors
✔ Proper logging & monitoring
✔ No try-catch abuse in controllers

🔹 Conclusion

Exception handling is not optional in ASP.NET Core—it is a fundamental design requirement.

📌 Key Takeaways

  • Middleware handles global exceptions
  • Filters handle MVC-specific exceptions
  • Therefore, using both approaches creates secure, scalable, and maintainable applications.

👉 Read our detailed guides on Middleware vs Filters and How to Fix CORS Error in ASP.NET Core API to deepen your understanding.

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