Locating resources

Loading the configuration normally starts with a search for resources – in most cases: files. This can be done with the FileLocator:

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use Symfony\Component\Config\FileLocator;

$configDirectories = array(__DIR__.'/app/config');

$locator = new FileLocator($configDirectories);
$yamlUserFiles = $locator->locate('users.yml', null, false);

The locator receives a collection of locations where it should look for files. The first argument of locate() is the name of the file to look for. The second argument may be the current path and when supplied, the locator will look in this directory first. The third argument indicates whether or not the locator should return the first file it has found, or an array containing all matches.

Resource loaders

For each type of resource (Yaml, XML, annotation, etc.) a loader must be defined. Each loader should implement LoaderInterface or extend the abstract FileLoader class, which allows for recursively importing other resources:

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use Symfony\Component\Config\Loader\FileLoader;
use Symfony\Component\Yaml\Yaml;

class YamlUserLoader extends FileLoader
{
    public function load($resource, $type = null)
    {
        $configValues = Yaml::parse($resource);

        // ... handle the config values

        // maybe import some other resource:

        // $this->import('extra_users.yml');
    }

    public function supports($resource, $type = null)
    {
        return is_string($resource) && 'yml' === pathinfo(
            $resource,
            PATHINFO_EXTENSION
        );
    }
}

Finding the right loader

The LoaderResolver receives as its first constructor argument a collection of loaders. When a resource (for instance an XML file) should be loaded, it loops through this collection of loaders and returns the loader which supports this particular resource type.

The DelegatingLoader makes use of the LoaderResolver. When it is asked to load a resource, it delegates this question to the LoaderResolver. In case the resolver has found a suitable loader, this loader will be asked to load the resource:

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use Symfony\Component\Config\Loader\LoaderResolver;
use Symfony\Component\Config\Loader\DelegatingLoader;

$loaderResolver = new LoaderResolver(array(new YamlUserLoader($locator)));
$delegatingLoader = new DelegatingLoader($loaderResolver);

$delegatingLoader->load(__DIR__.'/users.yml');
/*
The YamlUserLoader will be used to load this resource,
since it supports files with a "yml" extension
*/