What is an HttpHandler in ASP.NET

In the simplest terms, an ASP.NET HttpHandler is a class that implements the System.Web.IHttpHandler interface.

ASP.NET HTTPHandlers are responsible for intercepting requests made to your ASP.NET web application server. They run as processes in response to a request made to the ASP.NET Site. The most common handler is an ASP.NET page handler that processes .aspx files. When users request an .aspx file, the request is processed by the page through the page handler.

ASP.NET offers a few default HTTP handlers:

• Page Handler (.aspx): handles Web pages
• User Control Handler (.ascx): handles Web user control pages
• Web Service Handler (.asmx): handles Web service pages
• Trace Handler (trace.axd): handles trace functionality

You can create your own custom HTTP handlers that render custom output to the browser. Typical scenarios for HTTP Handlers in ASP.NET are for example

• delivery of dynamically created images (charts for example) or resized pictures.
• RSS feeds which emit RSS-formated XML

You implement the IHttpHandler interface to create a synchronous handler and the IHttpAsyncHandler interface to create an asynchronous handler. The interfaces require you to implement the ProcessRequest method and the IsReusable property.

The ProcessRequest method handles the actual processing for requests made, while the Boolean IsReusable property specifies whether your handler can be pooled for reuse (to increase performance) or whether a new handler is required for each request.

An HttpHandler (or IHttpHandler) is basically anything that is responsible for serving content. An ASP.NET page (aspx) is a type of handler.

You might write your own, for example, to serve images etc from a database rather than from the web-server itself, or to write a simple POX service (rather than SOAP/WCF/etc)

HttpHandler Example,

HTTP Handler in ASP.NET 2.0

A handler is responsible for fulfilling requests from a browser. Requests that a browser manages are either handled by file extension or by calling the handler directly.The low level Request and Response API to service incoming Http requests are Http Handlers in Asp.Net. All handlers implement the IHttpHandler interface, which is located in the System.Web namespace. Handlers are somewhat analogous to Internet Server Application Programming Interface (ISAPI) extensions.

You implement the IHttpHandler interface to create a synchronous handler and the IHttpAsyncHandler interface to create an asynchronous handler. The interfaces require you to implement the ProcessRequest method and the IsReusable property. The ProcessRequest method handles the actual processing for requests made, while the Boolean IsReusable property specifies whether your handler can be pooled for reuse to increase performance or whether a new handler is required for each request.

The .ashx file extension is reserved for custom handlers. If you create a custom handler with a file name extension of .ashx, it will automatically be registered within IIS and ASP.NET. If you choose to use an alternate file extension, you will have to register the extension within IIS and ASP.NET. The advantage of using an extension other than .ashx is that you can assign multiple file extensions to one handler.

Configuring HTTP Handlers

The configuration section handler is responsible for mapping incoming URLs to the IHttpHandler or IHttpHandlerFactory class. It can be declared at the computer, site, or application level. Subdirectories inherit these settings.Administrators use the tag directive to configure the section. directives are interpreted and processed in a top-down sequential order. Use the following syntax for the section handler:

Creating HTTP Handlers

To create an HTTP handler, you must implement the IHttpHandler interface. The IHttpHandler interface has one method and one property with the following signatures:void ProcessRequest(HttpContext);bool IsReusable {get;}