What is an HttpHandler in ASP.NET? Why and how is it used?

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