Comments on: A simple Filter Chain example in PHP 5

By: Matthijs

Matthijs — Sat, 12 Apr 2008 07:12:38 +0000

Wow, that’s a pretty cool piece of code. And excellent write-down, thanks. Makes me want to use this somewhere immediately.

By: chris

chris — Sat, 08 Sep 2007 09:02:09 +0000

I should point out also that this particluar example is run-once, because it uses array_shift which actually reduces the array size as it goes. If you need to repeatedly run the same filter chain you’d have to use iteration with a little extra logic.

By: chris

chris — Sat, 08 Sep 2007 08:57:52 +0000

Yes, sure :)

Back to my FrontController example. You may want to switch from using the unclean form index.php?module=aModule&action=myAction in the URL, to parsing out something like index.php/aModule/myAction and populating the request with the appropriate values.

For the FrontController to work without any prior knowledge of this aesthetic modification you need to ensure the request has been modified as early as possibe. The best way to do this is the place your request mapping logic in a filter chain which runs before the FrontController is ever reached.

Imagine I change the FilterChain to allow something to explictly run at the end of the chain (I’ll pass it to the constructor here).

$chain = new FilterChain(new FrontController());

$chain->addFilter(new RequestMapper());

$chain->doFilter(new Request(), new Response());

Now our RequestMapper class can read the REQUEST_URI value and determine what parameters to put in the request.

This is a typical use of the filter chain pattern and one you’ll see in some PHP frameworks (and in J2EE as standard).

Ideally you’d have a configuration file which allows filters to be specified loosely :)

By: Jeffery Fernandez

Jeffery Fernandez — Sat, 08 Sep 2007 06:15:23 +0000

Hey Chris,

Just wondering what real world example can this pattern be used in? Can you suggest some? Thanks

By: Bramus!

Bramus! — Mon, 20 Aug 2007 08:28:30 +0000

Yet again an awesome article Chris! Thanks!