Umbraco "Legacy URL" IContentFinder

global.asax.cs

using System;
using System.Web.Routing;
using Umbraco.Web;
using Umbraco.Web.Routing;
 
// as per http://maffrigby.com/using-custom-routes-in-umbraco/
 
namespace MyUmbraco
{
    public class MyUmbracoApplication : UmbracoApplication
    {
        //protected override void OnApplicationStarted(object sender, EventArgs e)
        //{
        //    base.OnApplicationStarted(sender, e);
        //    RouteConfig.RegisterRoutes(RouteTable.Routes);
        //}
        
        protected override void OnApplicationStarting(object sender, EventArgs e)
        {
            ContentFinderResolver.Current.RemoveType<ContentFinderByNotFoundHandlers>();
            ContentLastChanceFinderResolver.Current.SetFinder(new MyContentFinder());
            base.OnApplicationStarting(sender, e);
        }
    }
}

MyContentFinder.cs

using Umbraco.Core;
using Umbraco.Core.Services;
using Umbraco.Web;
using Umbraco.Web.Routing;
using umbraco;
using System.Linq;
 
namespace MyUmbraco
{

    // via https://creativewebspecialist.co.uk/2013/08/07/the-new-way-to-do-a-404-umbraco-handler/
    public class MyContentFinder : IContentFinder
    {
        const int NOT_FOUND_NODE = 1111; // THIS IS THE NODE FOR MY 404 PAGE
        const int REDIRECT_TYPE = 302; // TODO: Set to 301 for permanent/SEO purposes when you're more comfortable
        const string LEGACY_URL_FIELD = "myLegacyUrl";
        const string HOME_DOCTYPE = "myHomePage";
        readonly string[] IGNORED_PATTERNS = new string[] { ".png", ".jpg", ".gif", ".pdf" };
 
        public bool TryFindContent(PublishedContentRequest contentRequest)
        {
            //Check request is a 404
            if (contentRequest.Is404)
            {
                var reqPath = contentRequest.Uri.AbsolutePath;
                var notFoundNode = contentRequest.RoutingContext.UmbracoContext.ContentCache.GetById(NOT_FOUND_NODE);
                var home = contentRequest.RoutingContext.UmbracoContext.ContentCache.GetAtRoot().Single(x => x.DocumentTypeAlias == HOME_DOCTYPE);
 
                //(don't waste db search on asset requests etc)
                if (!IGNORED_PATTERNS.Any(pattern => reqPath.Contains(pattern))) {
                    // search DB for legacy URL that matches content request
                    var reqPathSearch = reqPath.ToLowerInvariant().Replace("/", "");
                    var legacyNode = home.Descendants()
                                    .DefaultIfEmpty(notFoundNode)
                                    .Where(d=>d.HasProperty(LEGACY_URL_FIELD))
                                    .FirstOrDefault(x =>
                                        reqPathSearch == x.GetPropertyValue<string>(LEGACY_URL_FIELD).ToLowerInvariant().Replace("/", "").Replace(".aspx","").Replace(".htm","")
                                    );
                   
                    if(legacyNode != null && legacyNode != notFoundNode) {
                        // if we have one, do a redirect
                        contentRequest.SetRedirect(legacyNode.Url, REDIRECT_TYPE);
                        return contentRequest.PublishedContent != null;
                    }
                }
 
                // default to 404
                contentRequest.SetResponseStatus(404, "404 Page Not Found");
                contentRequest.PublishedContent = notFoundNode;
            }
 
            return contentRequest.PublishedContent != null;
        }
    }
}