URL Rewriter

rewritemap.config

<rewriteMaps>
  <rewriteMap name="StaticRedirects">
    <add key="old_url" value="new_url" />
  </rewriteMap>
</rewriteMaps>

urlrewriter.cs

//1) We declare a dictionary to store the content of the rewritemap.config
private static IDictionary<string, string> rewriteMaps;

//2) Next, we add the following code inside Application_Start in your Global.asax.cs
//This will parse the config file and load it to a dictionary which ensures the uniqueness of each source URL.
//Feel free to extract this to a separate method to keeps thing clean.
protected void Application_Start(object sender, EventArgs e)
{           
    rewriteMaps = XDocument.Load(Server.MapPath("~/rewriteMaps.config"))
        .Element("rewriteMaps")
        .Element("rewriteMap")
        .Elements("add")
        .ToDictionary(
            el => el.Attribute("key").Value,
            el => el.Attribute("value").Value);
}

//3) Finally perform the redirects (in our case 301s) when needed in the appropriate spot in the ASP.NET lifecycle.
//Feel free to extract this to a seperate method as well.
protected void Application_BeginRequest(object sender, EventArgs e)
{
    var httpApplication = sender as HttpApplication;

    if (httpApplication != null)
    {
        string requestPath = httpApplication.Context.Request.Path;

        if(rewriteMaps.ContainsKey(requestPath))
        {
            HttpContext.Current.Response.RedirectPermanent(rewriteMaps[requestPath]);
        }
    }
}