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.
1Imports System.Text.RegularExpressions
2Imports System.Web
3
4Namespace Core.Handlers
5
6 Public Class BlogRedirectHandler
7 Implements IHttpHandler
8
9 Private Shared m_Patterns() As String = {"/archive/*", _
10 "/Tag/*/default.aspx", _
11 "/category/*"}
12
13 Public Shared Function IsValidToRun(ByVal context As System.Web.HttpContext, _
14 ByVal requestType As String, _
15 ByVal virtualPath As String, _
16 ByVal path As String) As Boolean
17 For Each p In m_Patterns
18 If Regex.IsMatch(context.Request.Url.ToString, p) Then Return True
19 Next
20 Return False
21 End Function
22
23 Public ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
24 Get
25 Return True
26 End Get
27 End Property
28
29 Public Sub ProcessRequest(ByVal context As System.Web.HttpContext) Implements IHttpHandler.ProcessRequest
30 Dim oldurl As String = context.Request.Url.ToString
31 If oldurl.Contains("/archive/") Then
32 Dim newurl As String = "http://blog.hinshelwood.com" & context.Request.Url.AbsolutePath
33 context.Response.StatusCode = System.Net.HttpStatusCode.MovedPermanently ' permanent HTTP 301
34 context.Response.RedirectLocation = newurl
35 context.Response.StatusDescription = "Moved Permanently"
36 context.Response.ContentType = "text/html"
37 context.Response.Write("<html><head><title>Object Moved</title></head><body>")
38 context.Response.Write("<h2>Object moved to <a href=" & newurl & " >here</a>.</h2>")
39 context.Response.Write("</body></html>")
40 context.Response.End()
41 End If
42
43 End Sub
44
45 End Class
46
47End 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.
1Imports System.Web
2
3Namespace Core.Handlers
4
5 Public Class CustomPageHandlerFactory
6 Inherits PageHandlerFactory
7
8 Public Overrides Function GetHandler(ByVal context As System.Web.HttpContext, _
9 ByVal requestType As String, _
10 ByVal virtualPath As String, _
11 ByVal path As String) As IHttpHandler
12 If BlogRedirectHandler.IsValidToRun(context, requestType, virtualPath, path) Then
13 Return New BlogRedirectHandler
14 Else
15 Return MyBase.GetHandler(context, requestType, virtualPath, path)
16 End If
17 End Function
18 End Class
19
20End 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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