Loading Resources
Loaders populate the application's configuration from different sources like YAML files. The Config component defines the interface for such loaders. The Dependency Injection and Routing components come with specialized loaders for different file formats.
Locating Resources
Loading the configuration normally starts with a search for resources, mostly files. This can be done with the FileLocator:
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use Symfony\Component\Config\FileLocator;
$configDirectories = [__DIR__.'/config'];
$fileLocator = new FileLocator($configDirectories);
$yamlUserFiles = $fileLocator->locate('users.yaml', null, false);The locator receives a collection of locations where it should look for
files. The first argument of locate() is the name of the file to look
for. The second argument may be the current path and when supplied, the
locator will look in this directory first. The third argument indicates
whether or not the locator should return the first file it has found or
an array containing all matches.
Resource Loaders
For each type of resource (YAML, XML, attributes, etc.) a loader must be defined. Each loader should implement LoaderInterface or extend the abstract FileLoader class, which allows for recursively importing other resources:
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namespace Acme\Config\Loader;
use Symfony\Component\Config\Loader\FileLoader;
use Symfony\Component\Yaml\Yaml;
class YamlUserLoader extends FileLoader
{
public function load($resource, $type = null): void
{
$configValues = Yaml::parse(file_get_contents($resource));
// ... handle the config values
// maybe import some other resource:
// $this->import('extra_users.yaml');
}
public function supports($resource, $type = null): bool
{
return is_string($resource) && 'yaml' === 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 Acme\Config\Loader\YamlUserLoader;
use Symfony\Component\Config\Loader\DelegatingLoader;
use Symfony\Component\Config\Loader\LoaderResolver;
$loaderResolver = new LoaderResolver([new YamlUserLoader($fileLocator)]);
$delegatingLoader = new DelegatingLoader($loaderResolver);
// YamlUserLoader is used to load this resource because it supports
// files with the '.yaml' extension
$delegatingLoader->load(__DIR__.'/users.yaml');