tech·nic·al·ly agile
IHandlerFactory
Discover how to implement a BlogRedirectHandler in ASP.NET to manage URL redirects effectively, ensuring a smooth transition for your users.
https://nkdagility.com/resources/kYNSKaqUYb7
As you have probably noticed I have moved URL’s (sorry to all you feed readers with the duplicate entries). The reason I moved my blog was to free up the http://hinshelwood.com URL for use as a personal site that then links to my blog. When you do this you need to consider all of your current users, bookmarks, feeds, links and all that malarkey.
So, I created a WebRedirect (thanks to DynDNS.org) that means that all hinshelwood.com traffic is automatically redirected to blog.hinshelwood.com including all of the sub pages. This is fine until I actually put up a site on hinshelwood.com and brake all of the links… HttpHandler to the rescue…
The first step was to create a “BlogRedirectHandler” to redirect all of those pesky URL’s to the new site.
Imports System.Text.RegularExpressions
Imports System.Web
Namespace Core.Handlers
Public Class BlogRedirectHandler
Implements IHttpHandler
Private Shared m_Patterns() As String = {"/archive/*", _
"/Tag/*/default.aspx", _
"/category/*"}
Public Shared Function IsValidToRun(ByVal context As System.Web.HttpContext, _
ByVal requestType As String, _
ByVal virtualPath As String, _
ByVal path As String) As Boolean
For Each p In m_Patterns
If Regex.IsMatch(context.Request.Url.ToString, p) Then Return True
Next
Return False
End Function
Public ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
Get
Return True
End Get
End Property
Public Sub ProcessRequest(ByVal context As System.Web.HttpContext) Implements IHttpHandler.ProcessRequest
Dim oldurl As String = context.Request.Url.ToString
If oldurl.Contains("/archive/") Then
Dim newurl As String = "http://blog.hinshelwood.com" & context.Request.Url.AbsolutePath
context.Response.StatusCode = System.Net.HttpStatusCode.MovedPermanently ' permanent HTTP 301
context.Response.RedirectLocation = newurl
context.Response.StatusDescription = "Moved Permanently"
context.Response.ContentType = "text/html"
context.Response.Write("<html><head><title>Object Moved</title></head><body>")
context.Response.Write("<h2>Object moved to <a href=" & newurl & " >here</a>.</h2>")
context.Response.Write("</body></html>")
context.Response.End()
End If
End Sub
End Class
End Namespace
This little piece of code has two important pieces, the “IsValidToRun” which makes sure that we need to run it, and the “ProcessRequest” method that does the actual dog work of the redirect.
I have chosen to use a “MovedPermanently“ status so that the search engines will catch on more quickly and the new URL should quite quickly replace the old.
If we just added this handler to the web application we would loose all of our .aspx pages and only see a blank page for those that are not valid for this handler.
To handle this the easiest way is to inherit from the existing “PageHandlerFactory” that is the default in ASP.NET.
Imports System.Web
Namespace Core.Handlers
Public Class CustomPageHandlerFactory
Inherits PageHandlerFactory
Public Overrides Function GetHandler(ByVal context As System.Web.HttpContext, _
ByVal requestType As String, _
ByVal virtualPath As String, _
ByVal path As String) As IHttpHandler
If BlogRedirectHandler.IsValidToRun(context, requestType, virtualPath, path) Then
Return New BlogRedirectHandler
Else
Return MyBase.GetHandler(context, requestType, virtualPath, path)
End If
End Function
End Class
End Namespace
Then all we need to do is call our IsValidToRun method and either run the base (default) GetHandler or return our new handler…
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