How and When to Use PSR-4 Autoloading in Your Craft Plugins

If you’re developing a reasonably sophisticated Craft plugin, chances are you’ll have a lot of class files which don’t really fit into the “standard” Craft plugin sub-directories of models, records, and so forth.

In this situation, you need a way to easily loading your “non-standard” classes as-and-when they’re required. You could faff about with require statements, but what is this, the 90s?

A better solution is to use PSR-4 autoloading, and by the end of this article you’ll know how to do exactly that.

When to use PSR-4 autoloading

Before we get into how to use PSR-4 autoloading, let’s first clarify when you need to use it.

Craft assumes that you’ve organised your plugin into models, records, services, and so forth as per the documentation, and takes care of the grunt work of loading these files for you.

Specifically, if your class resides in any of the following directories within your plugin1, you don’t need to need to use PSR-4 autoloading; you just need to ensure that your class name follows the naming conventions described in the documentation:

  • controllers/
  • enums/
  • fieldtypes
  • helpers/
  • models/
  • records/
  • services/
  • validators/
  • variables/
  • widgets/

Assuming your code resides within the Craft namespace (which it will, most of the time), you can access the classes loaded from these directories by name. For example:

<?php namespace Craft;

$exampleModel = new PluginName_ExampleModel;

If your code resides in a different namespace, you just need to import the desired class with the use keyword:

<?php namespace Some\Other\Namespace;

use Craft\PluginName_ExampleModel;

$exampleModel = new PluginName_ExampleModel;

If you need to a load class which doesn’t live in one of the aforementioned directories, that’s where PSR-4 autoloading comes in.

How to implement PSR-4 autoloading

This isn’t a deep technical dive into PSR-4 autoloading. Rather, it’s a simple step-by-step guide to help you get up and running.

With that in mind, we’re going to cover four things:

  1. Namespacing your classes.
  2. Telling Composer where to find your classes.
  3. Generating the Composer autoloader.
  4. Using the Composer autoloader in your plugin.

For the purposes of this article, we’re going use an imaginary plugin called “LocateMe”. LocateMe needs to make use of a “Logger” class, which lives in a “utilities” directory.

So, our basic plugin directory looks like this:

|- locateme/
   |- LocateMePlugin.php
   |- utilities/
      |- Logger.php

Step 1: Namespace your classes

PSR-4 assumes that the classes we wish to autoload are correctly namespaced. As such, we need to add a namespace declaration to the top of our “Logger” class file.

Here’s what that looks like:

<?php namespace LocateMe\Utilities;

class Logger

Step 2: Tell Composer where to find your classes

We configure Composer using a composer.json file, located in the root of our plugin directory (alongside LocateMePlugin.php).

Our updated plugin directory looks like this:

|- locateme/
   |- composer.json
   |- LocateMePlugin.php
   |- utilities/
      |- Logger.php

composer.json includes a section which tells Composer where within the filesystem the classes in the LocateMe\Utilities namespace reside2.

Here’s how that looks in practise:

  "autoload": {
    "psr-4": {
      "LocateMe\\Utilities\\": "utilities/"

In other words, we’re telling Composer to look for our utility classes in our plugin’s utilities directory.

Step 3: Generate your Composer autoloader

Once we’ve created our composer.json file, we need to tell Composer to generate the “autoloader”. Assuming you already have Composer installed, this is easy:

$> composer dump-autoload --optimize

Upon receiving this edict, Composer will generate a new vendor/composer directory, containing a number of autoload_*.php classes.

Your plugin directory will now look something like this:

|- locateme/
   |- composer.json
   |- LocateMePlugin.php
   |- utilities/
      |- Logger.php
   |- vendor
      |- autoload.php
      |- composer/
         |- autoload_classmap.php
         |- autoload_namespaces.php
         |- autoload_psr4.php
         |- autoload_real.php
         |- ClassLoader.php
         |- installed.json

Step 4: Use the Composer autoloader in your plugin

The final step to implementing PSR-4 autoloading in your plugins is to ensure that your plugin loads the Composer-generated autoload.php file.

For this, we use the trusty old require_once statement:

<?php namespace Craft;

class LocateMePlugin extends BasePlugin
    public function init()
        require_once __DIR__ .'/vendor/autoload.php';

That’s it. The autoloader will now be available every time we use our plugin, allowing us to load our classes with the use statement.

For example, let’s say our plugin has an “address” service, which needs to access the Logger utility. Here’s how that might look:

<?php namespace Craft;

use LocateMe\Utilities\Logger;

class LocateMe_AddressService extends BaseApplicationComponent
    private $logger;

    public function __construct()
        $this->logger = new Logger;

    public function convertAddressToLocation($street, $zip)
        // Do stuff.

        $this->logger->log('Converted address: ' . $street);


And that is everything you need to know about using PSR-4 autoloading in your plugins.

If you’d like to dig a little deeper, Laracasts has a nice (and free) gentle introduction to PSR-4, and the official Composer website documents the composer.json schema in exhaustive detail.

  1. Autoloading is handled by the PluginsService::_autoloadPluginClasses method. The “autoloadable” classes are defined in the common.php config file↩︎

  2. In the words of the Composer documentation, “Under the psr-4 key you define a mapping from namespaces to paths, relative to the package root.” ↩︎

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