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

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ICSM Computer · Answer

In ASP.NET MVC/Web API, filters are attributes that allow you to execute
custom logic before or after controller actions run. They are a core part of the request pipeline and are used for cross-cutting concerns like
logging, authentication, exception handling, etc.
Filters are declarative attributes applied to controllers or actions to
intercept and process HTTP requests/responses at specific points in the execution pipeline.
Types of Filters in ASP.NET MVC / Web API
Filter Type
Purpose
Runs
Authorization Filter
Checks if the user is authorized to access the resource
Before controller/action
Action Filter
Runs logic before and/or after the action executes
Before and after action method
Result Filter
Runs logic before and after the response is returned
Before and after result execution (e.g., ViewResult)
Exception Filter
Handles unhandled exceptions globally
When an exception occurs
Authentication Filter (Web API)
Authenticates the request
Before authorization filter
1. Authorization Filter
Use Case:
Role-based access controlAPI key checks
Example:
[Authorize(Roles = "Admin")]
public ActionResult AdminDashboard() { ... }
2. Action Filter
Use Case:
Logging, tracking performanceValidating inputModifying input/output
Example:
public class LogActionAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        // Log before action executes
    }
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        // Log after action executes
    }
}
Usage:
[LogAction]
public ActionResult Index() { ... }
3. Result Filter
Use Case:
Modify or log response after the action executes but before renderingAdd custom headers to response
Example:
public class AddHeaderAttribute : ResultFilterAttribute
{
    public override void OnResultExecuting(ResultExecutingContext filterContext)
    {
        filterContext.HttpContext.Response.Headers["X-App-Version"] = "1.0";
    }
}
4. Exception Filter
Use Case:
Global error handlingLogging exceptionsShowing friendly error pages
Example:
public class CustomExceptionFilter : FilterAttribute, IExceptionFilter
{
    public void OnException(ExceptionContext filterContext)
    {
        // Log or handle exception
        filterContext.ExceptionHandled = true;
    }
}
5. Authentication Filter (Web API only)
Use Case:
Custom authentication logicToken or API key authentication
Web API supports IAuthenticationFilter interface (MVC does not have this filter type).
Applying Filters
Globally: via FilterConfig.csController-level: on controller classAction-level: on specific action method
// Global
filters.Add(new HandleErrorAttribute());
// Controller-level
[CustomLog]
public class ProductsController : Controller { ... }
// Action-level
[Authorize]
public ActionResult SecureArea() { ... }
Summary
Filter Type
Key Use Cases
Authorization
User/role validation
Action
Logging, timing, input validation
Result
Modifying output, headers
Exception
Centralized error handling
Authentication (Web API)
Token-based or custom authentication

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

Anubhav Kumar

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1 Answers

Types of Filters in ASP.NET MVC / Web API

1. Authorization Filter

Use Case:

Example:

2. Action Filter

Use Case:

Example:

3. Result Filter

Use Case:

Example:

4. Exception Filter

Use Case:

Example:

5. Authentication Filter (Web API only)

Use Case:

Applying Filters

Summary

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Filter Type	Purpose	Runs
Authorization Filter	Checks if the user is authorized to access the resource	Before controller/action
Action Filter	Runs logic before and/or after the action executes	Before and after action method
Result Filter	Runs logic before and after the response is returned	Before and after result execution (e.g., ViewResult)
Exception Filter	Handles unhandled exceptions globally	When an exception occurs
Authentication Filter (Web API)	Authenticates the request	Before authorization filter

Filter Type	Key Use Cases
Authorization	User/role validation
Action	Logging, timing, input validation
Result	Modifying output, headers
Exception	Centralized error handling
Authentication (Web API)	Token-based or custom authentication