.NetCore MiddleWare Exception Handling Example

.NetCore MiddleWare Exception Handling Example

In .NET Core, middleware allows you to handle exceptions centrally instead of writing multiple try-catch blocks in every controller.

1. Centralized Error Handling
2. Consistent Error Response Format
3. Logs every exception automatically
4. Easier maintenance

Simple Custom Middleware Example

Step 1: Create Middleware Class

using Microsoft.AspNetCore.Http;
using System;
using System.Net;
using System.Threading.Tasks;

public class ExceptionMiddleware
{
    private readonly RequestDelegate _next;

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

    public async Task InvokeAsync(HttpContext httpContext)
    {
        try
        {
            await _next(httpContext); // Call next middleware or endpoint
        }
        catch (Exception ex)
        {
            await HandleExceptionAsync(httpContext, ex);
        }
    }

    private static Task HandleExceptionAsync(HttpContext context, Exception exception)
    {
        // Log the exception (you can integrate Serilog/NLog here)
        Console.WriteLine($"Something went wrong: {exception.Message}");

        context.Response.ContentType = "application/json";
        context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;

        return context.Response.WriteAsync(new
        {
            StatusCode = context.Response.StatusCode,
            Message = "Internal Server Error. Please try again later.",
            Detailed = exception.Message // Optional — remove in production
        }.ToString());
    }
}

Step 2: Register Middleware in Program.cs or Startup.cs

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

// Register the middleware
app.UseMiddleware();

app.MapControllers();
app.Run();

Step 3: Test it

Create a sample controller that throws an exception.

[ApiController]
[Route("api/[controller]")]
public class TestController : ControllerBase
{
    [HttpGet("error")]
    public IActionResult GetError()
    {
        throw new Exception("This is a test exception!");
    }
}

Now, when you browse to: https://localhost:5001/api/test/error

You’ll get a JSON response like:

{
  "StatusCode": 500,
  "Message": "Internal Server Error. Please try again later.",
  "Detailed": "This is a test exception!"
}

Using Built-in Exception Handler Middleware

app.UseExceptionHandler("/error");