Using ColdFusion to Handle HTTP 404 Page Not Found Errors

This article will not address the onMissingTemplate method which only runs when a CFML page does not exist (i.e., wwwroot/directory/thisPageDoesNotExist.cfm). In addition, this article will not address using custom headers or a .htaccess file with Apache. This article will address those other "page not found" errors often found in Windows hosted environments.

Let's start by assuming someone tries to visit www.yourdomain.com/thisDirectoryDoesNotExist, or www.yourdomain.com/thisPageDoesNotExist.html and neither the directory, nor the page actually exist on your site. Or, better yet, you've just spent months building a new, dynamic site for a client using ColdFusion and their old site was an old, yucky plain HTML site with pages everywhere. Now, your client, who's a little savvy in the SEO department, (that's search engine optimization for you non-seo-knowing folk), has requested you setup redirects for each of his old pages to the new ones you've created.

If you're anything like me, I used to dread the thought of taking care of this. I used to spend a ton of time on this by creating a separate page for each of the "old" pages and directories, then using either JavaScript to handle the redirects (if the old page was vanilla HTML) or the "old" dynamic language (i.e., ASP, PHP, etc.) to create custom headers, etc. Regardless, it was a major pain to do this, especially because it cluttered my site with a bunch of extra files that were essentially useless.

Then, I had one of those "light bulb moments." I thought, "Hey, I'm already using a custom tag to handle 'page not found' requests, so if I could somehow capture the requested page, match it against a list of 'known-to-be-missing' pages, then I could code a way to forward to the 'new' destination." Sounds simple enough, eh?

For those of us using a shared-host provider such as CrystalTech or HostMySite, they're kind enough to allow us to create custom pages to handle certain HTTP errors, such as 404. It's usually found in the service provider's "control panel" under something like "IIS > Custom Error Pages." Once there, you usually have three options to pick from: 1) Default, 2) File and 3) URL. In most cases, "Default" loads the standard error page provided by our friends at Microsoft. "File" is just that, a flat, static, HTML page. What we want to use is "URL," so that we can use ColdFusion to help us out. In fact, I'll be nice and even provide a link to both CrystalTech's process and HostMySite's process. But before you do this, you'll need to at least set up a .CFM file somewhere on your site so you know what to enter into the URL path, right? So for now, let's assume you've created a file call "404.cfm" and placed in a directory structure like so: "/extensions/customtags/404.cfm"

So, assuming you've got your custom error page setup properly, you will now be able to capture a query string which contains the "requested URL" that really didn't exist. The easiest way to test this would be to enter this code onto your 404.cfm file, upload it to your site, then try a non-existent directory such as www.yourdomain.com/abcd/.

You should see something like this: "404;http://www.yourdomain.com:80/abcd/"

There's some great information coming through here. First, you'll notice that you're receiving the error number (404). Next, you'll see your domain also includes the port number being used. For example, if using HTTP, then you will most likely see the number 80, or if your using HTTPS, then you should probably see 443.

For this next part, you might have to adjust this if you ever use a colon ( : ) in your directory or page naming conventions (this is not generally used, so I wouldn't expect this to be much of an issue).

Look again at the query string that we've been given, what we really want to grab is everything after the port number. Or, the absolute path to the page or directory being requested. So this is what I came up with:

So, now if we use the same url we tried earlier, I should see something like: "/abcd/" Now, I've got a variable that I can use to match against to see if this is a "known" directory or page from our old site. Now we just need something to handle the "matching" and then receive a response to make decisions against.

Luckily, I've created a rather simple .CFC which can easily be modified to accommodate any "known" directories and/or pages, including .ASP, .PHP, etc.

Now, we just need to invoke the ColdFusion Component to see if there's a match.

As you can see, if no match has been found, a variable called "newPage" is merely left blank. So, now we can write a little more code to accommodate both "known-to-be-missing" and "truly-unknown-and-really-missing" directories and pages. If a page is "known-to-be-missing", I can pass a search engine friendly header so that everything runs as smoothly as possible.

Here's the final document, aside from the .CFC above which should be kept separate.

As you can see, I like to use a custom tag to handle the layout of my pages, etc. You can find out more about that at Raymond Camden's site.

I hope this helps a fellow ColdFusion developer. Thanks for reading!