How do you handle exceptions globally in an ASP.NET Core application?

Handling exceptions globally in an ASP.NET Core application is essential for maintaining a consistent error response and ensuring that sensitive information is not exposed to the client. ASP.NET Core provides several mechanisms to manage exceptions globally, including middleware and filters. Here’s a detailed explanation of how to implement global exception handling effectively.

1. Using Middleware for Global Exception Handling

Creating custom middleware is one of the most common ways to handle exceptions globally in an ASP.NET Core application.

Steps to Implement Global Exception Handling Middleware:

1. Create Custom Middleware: You can create a middleware class that intercepts requests and handles exceptions.

   
   using Microsoft.AspNetCore.Http;
   using Microsoft.Extensions.Logging;
   using System;
   using System.Net;
   using System.Threading.Tasks;
   using System.Text.Json;
   
   public class ExceptionHandlingMiddleware
   {
       private readonly RequestDelegate _next;
       private readonly ILogger<ExceptionHandlingMiddleware> _logger;
   
       public ExceptionHandlingMiddleware(RequestDelegate next, ILogger<ExceptionHandlingMiddleware> logger)
       {
           _next = next;
           _logger = logger;
       }
   
       public async Task InvokeAsync(HttpContext context)
       {
           try
           {
               await _next(context); // Call the next middleware in the pipeline
           }
           catch (Exception ex)
           {
               await HandleExceptionAsync(context, ex);
           }
       }
   
       private Task HandleExceptionAsync(HttpContext context, Exception exception)
       {
           _logger.LogError(exception, "An unhandled exception occurred.");
           
           context.Response.ContentType = "application/json";
           context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
   
           var result = JsonSerializer.Serialize(new
           {
               error = "An unexpected error occurred. Please try again later."
           });
           return context.Response.WriteAsync(result);
       }
   }
   

2. Register Middleware: In the Startup class, register the middleware in the Configure method.

   
   public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
   {
       app.UseMiddleware<ExceptionHandlingMiddleware>(); // Register custom middleware
       
       // Other middleware registrations (e.g., app.UseRouting(), app.UseEndpoints())
   }
   

2. Using Exception Filters

Another approach is to use exception filters, which allow for centralized handling of exceptions at the action or controller level.

Steps to Implement Exception Filters:

1. Create an Exception Filter: Implement the IExceptionFilter interface to define your exception handling logic.

   
   using Microsoft.AspNetCore.Mvc;
   using Microsoft.AspNetCore.Mvc.Filters;
   using Microsoft.Extensions.Logging;
   
   public class CustomExceptionFilter : IExceptionFilter
   {
       private readonly ILogger<CustomExceptionFilter> _logger;
   
       public CustomExceptionFilter(ILogger<CustomExceptionFilter> logger)
       {
           _logger = logger;
       }
   
       public void OnException(ExceptionContext context)
       {
           _logger.LogError(context.Exception, "An error occurred while processing the request.");
   
           context.Result = new ObjectResult(new
           {
               error = "An unexpected error occurred. Please try again later."
           })
           {
               StatusCode = StatusCodes.Status500InternalServerError
           };
   
           context.ExceptionHandled = true; // Mark exception as handled
       }
   }
   

2. Register the Exception Filter: You can register the filter globally in the ConfigureServices method.

   
   public void ConfigureServices(IServiceCollection services)
   {
       services.AddControllers(options =>
       {
           options.Filters.Add<CustomExceptionFilter>(); // Register as a global filter
       });
   }
   

3. Using the Developer Exception Page (Development Environment)

For debugging purposes in the development environment, you can enable the Developer Exception Page, which provides detailed information about exceptions.

Steps to Enable Developer Exception Page:

1. Configure in Startup: In the Configure method, use the UseDeveloperExceptionPage method when the environment is set to Development.

   csharp
   public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
   {
       if (env.IsDevelopment())
       {
           app.UseDeveloperExceptionPage(); // Show detailed error pages in development
       }
       else
       {
           app.UseExceptionHandler("/Home/Error"); // Redirect to a generic error page in production
           app.UseHsts();
       }
       
       // Other middleware registrations (e.g., app.UseRouting(), app.UseEndpoints())
   }
   

Conclusion

By implementing global exception handling through middleware or filters in ASP.NET Core, you can ensure that exceptions are consistently logged and managed, providing a better experience for users and maintainers of the application. Additionally, using the Developer Exception Page during development helps in quickly identifying and resolving issues.