###1.创建一个自动加载的扩展类 *. 类在DependencyInjection命令空间下(通常文件位置位于DependencyInjection 目录下) *. 文件的命令是去掉Bundle的名称的后缀Bundle用Extension来替代(eg AppBundle --> AppExtesion)

该类需要实现ExtensionInterface接口；通常通过继承 Extension类来实现

// src/Acme/HelloBundle/DependencyInjection/AcmeHelloExtension.phpnamespace Acme\HelloBundle\DependencyInjection;use Symfony\Component\HttpKernel\DependencyInjection\Extension;use Symfony\Component\DependencyInjection\ContainerBuilder;class AcmeHelloExtension extends Extension{    public function load(array $configs, ContainerBuilder $container)    {        // ... you'll load the files here later    }}

###2. 手动注册一个扩展类 如果我们不遵守上面自动加载的约束；我们将要手动注册该扩展类；我们需要重写Bundle的getContainerExtension方法；该方法返回我们的扩展类的实例

use Acme\HelloBundle\DependencyInjection\UnconventionalExtensionClass;class AcmeHelloBundle extends Bundle{    public function getContainerExtension()    {        return new CustomerExtension();//自定义的扩展类    }}

自定义的扩展类；需要重写getAlias方法返回DI的别名;通常就是去掉Extension后缀的(eg AcmeHelloExtension-->acme_hello)class CustomerExtension extends Extension{    /**     * {@inheritdoc}     * load方法所有和extension相关的配置，服务将要被加载     *     */    public function load(array $configs, ContainerBuilder $container)    {        //有 YamlFileLoader, PhpFileLoader,IniFileLoader.        $loader = new Loader\YamlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));        $loader->load('services.yml');    }    public function getAlias()    {        return 'acme_hello';    }}