An ASP.NET HTTP handler is
the process (frequently referred to as the "endpoint") that runs in
response to a request made to an ASP.NET Web application. 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. You can create your own HTTP handlers that render custom
output to the browser.
The HttpHandler is a pre-processing
logic implementation blocks
and is the part of the ASP.NET request pipeline. Whenever the IIS Server recieves a request, it looks for an ISAPI filter(looking for the perticuler
httphandler to handle a perticuler extension) that is capable of handling web requests.
ASP.NET maps HTTP requests to HttpHandlers. Each HttpHandler enables processing of individual HTTP URLs or groups of URL extensions within an application.
Handlers
are considered to be more lightweight object than pages. That's why they are
used to serve dynamically-generated images, on-the-fly generated PDF-files and similar content to the web
browser.
below is an example (.ashx file)..
<%@ WebHandler Language="C#" Class="DownLoad" %>
using System;
using System.Web;
using System.Data;
using System.Data.SqlClient;
public class DownLoad : IHttpHandler {
CompCls ObjComp = new CompCls();
public void ProcessRequest(HttpContext context)
{
string conString = ObjComp.strCon;
SqlConnection con = new SqlConnection(conString);
string Proj = context.Request["id"];
SqlDataAdapter Ad = new SqlDataAdapter("SELECT Attachment,AttachmentFileName
FROM tblProjectsAttachment WHERE EntryId=@EntryId", con);
Ad.SelectCommand.Parameters.AddWithValue("@EntryId", Proj);
DataSet DS = new DataSet();
Ad.Fill(DS);
using (con)
{
con.Open();
byte[] file = (byte[])DS.Tables[0].Rows[0][0];
string Filename = DS.Tables[0].Rows[0][1].ToString();
try
{
context.Response.Clear();
context.Response.AddHeader
("Content-Disposition","inline;attachment;
filename=\"" + Filename + "\"");
context.Response.AddHeader("Content-Length",
file.Length.ToString());
context.Response.ContentType = "application/octet-stream";
context.Response.BinaryWrite(file);
context.Response.Flush();
}
catch (Exception ex)
{
context.Response.ContentType = "text/plain";
context.Response.Write(ex.Message);
}
}
}
public bool IsReusable {
get {
return false;
}
}
}
Want to more about http handler and http module go to below link (httphandler and httpmodule in asp.net)
http://c-sharp-corner.blogspot.in/2012/07/httphandler-and-httpmodule-in-aspnet.html
If We are hosting your application in IIS 7 then you have to do some additional setting in IIS 7 to be register httphandler and httpmodule in IIS 7 take look at this link below.
http://c-sharp-corner.blogspot.in/2012/06/Register httpmodules-and-httphandlers-in-iis-7.html