What are filters in ASP.NET MVC/Web API? Types and use cases?

Question

ICSM Computer · Answer

In ASP.NET MVC and ASP.NET Web API, 
filters are used to execute custom logic before or after specific stages in the request processing pipeline — such as
authentication, authorization, model binding, or action execution.
What Are Filters?
Filters are attributes (decorators) that allow code to run:
Before/After an action method executesBefore/After a result is returnedGlobally, per-controller, or per-action
They enable cross-cutting concerns like:
LoggingException handlingCachingAuthorizationPerformance monitoring
Types of Filters
Filter Type
Interface / Base Class
Runs When?
Common Use Case
Authorization Filter
IAuthorizationFilter (MVC) / AuthorizeAttribute
Before controller/action is invoked
User access control
Action Filter
IActionFilter / ActionFilterAttribute
Before and after action method executes
Logging, audit
Result Filter
IResultFilter / ResultFilterAttribute
Before and after action result executes
Modify view result
Exception Filter
IExceptionFilter / ExceptionFilterAttribute
On unhandled exceptions
Global error handling
Resource Filter (MVC Core/Web API Core)
IResourceFilter
Around entire request lifecycle
Caching, short-circuiting
Filter Execution Order
Authorization FiltersResource Filters (ASP.NET Core)Action FiltersResult FiltersException Filters (fires if exceptions occur)
Examples
1. Authorization Filter
[Authorize]
public class AdminController : Controller
{
    public ActionResult Dashboard() =andgt; View();
}
2. Custom Action Filter
public class LogActionFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext context)
    {
        // Log request data
    }
    public override void OnActionExecuted(ActionExecutedContext context)
    {
        // Log response or result
    }
}
Usage:
[LogActionFilter]
public ActionResult Index() =andgt; View();
3. Exception Filter
public class HandleExceptionFilter : FilterAttribute, IExceptionFilter
{
    public void OnException(ExceptionContext context)
    {
        // Log and handle
        context.ExceptionHandled = true;
        context.Result = new ViewResult { ViewName = "Error" };
    }
}
Filter Scopes
Filters can be applied at:
Global level (all controllers/actions)Controller levelAction level
// Global
GlobalFilters.Filters.Add(new LogActionFilter());
// Controller
[LogActionFilter]
public class ProductController : Controller { ... }
// Action
[LogActionFilter]
public ActionResult Details(int id) { ... }
Use Cases Summary
Use Case
Filter Type
Securing endpoints
Authorization Filter
Logging user activity
Action Filter
Modifying responses
Result Filter
Handling global errors
Exception Filter
Caching or short-circuit
Resource Filter

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What are filters in ASP.NET MVC/Web API? Types and use cases?

ICSM Computer

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1 Answers

What Are Filters?

Types of Filters

Filter Execution Order

Examples

1. Authorization Filter

2. Custom Action Filter

3. Exception Filter

Filter Scopes

Use Cases Summary

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Filter Type	Interface / Base Class	Runs When?	Common Use Case
Authorization Filter	`IAuthorizationFilter` (MVC) / `AuthorizeAttribute`	Before controller/action is invoked	User access control
Action Filter	`IActionFilter` / `ActionFilterAttribute`	Before & after action method executes	Logging, audit
Result Filter	`IResultFilter` / `ResultFilterAttribute`	Before & after action result executes	Modify view result
Exception Filter	`IExceptionFilter` / `ExceptionFilterAttribute`	On unhandled exceptions	Global error handling
Resource Filter (MVC Core/Web API Core)	`IResourceFilter`	Around entire request lifecycle	Caching, short-circuiting

Use Case	Filter Type
Securing endpoints	Authorization Filter
Logging user activity	Action Filter
Modifying responses	Result Filter
Handling global errors	Exception Filter
Caching or short-circuit	Resource Filter