The controller first requires the ``bootstrap.php.cache`` file, which bootstraps

the framework and registers the autoloader (see below). Then, it uses a kernel

class, ``AppKernel`` in this case, to bootstrap the application.

The controller first bootstraps the application using a kernel class (``AppKernel``

in this case). Then, it creates the ``Request`` object using the PHP's global

variables and passes it to the kernel. The last step is to send back to the user

the response contents returned by the kernel.

.. _the-app-dir:

(more on this later).

Autoloading is handled automatically via `Composer`_, which means that you

can use any PHP classes without doing anything at all! If you need more flexibility,

you can extend the autoloader in the ``app/autoload.php`` file. All dependencies

can use any PHP classes without doing anything at all! All dependencies

are stored under the ``vendor/`` directory, but this is just a convention.

You can store them wherever you want, globally on your server or locally

in your projects.

A bundle is kind of like a plugin in other software. So why is it called a

*bundle* and not a *plugin*? This is because *everything* is a bundle in

Symfony2, from the core framework features to the code you write for your

application. Bundles are first-class citizens in Symfony2. This gives you

the flexibility to use pre-built features packaged in third-party bundles

or to distribute your own bundles. It makes it easy to pick and choose which

features to enable in your application and optimize them the way you want.

And at the end of the day, your application code is just as *important* as

the core framework itself.

application.

Bundles are first-class citizens in Symfony2. This gives you the flexibility

to use pre-built features packaged in third-party bundles or to distribute your

own bundles. It makes it easy to pick and choose which features to enable in

your application and optimize them the way you want. And at the end of the day,

your application code is just as *important* as the core framework itself.

Registering a Bundle

In addition to the AcmeDemoBundle that was already talked about, notice

that the kernel also enables other bundles such as the FrameworkBundle,

DoctrineBundle, SwiftmailerBundle, and AsseticBundle bundle.

They are all partof the core framework.

DoctrineBundle, SwiftmailerBundle, and AsseticBundle bundle. They are all part

of the core framework.

Configuring a Bundle

Each bundle can be customized via configuration files written in YAML, XML, or

PHP. Have a look at the default configuration:

PHP. Have a look at the defaultSymfonyconfiguration:

..code-block::yaml

Each entry like ``framework`` defines the configuration for a specific bundle.

For example, ``framework`` configures the FrameworkBundle while ``swiftmailer``

configures the SwiftmailerBundle.

Eachfirst levelentry like ``framework``, ``twig`` or ``doctrine`` defines the

configuration for a specific bundle.For example, ``framework`` configures the

FrameworkBundle while ``swiftmailer``configures the SwiftmailerBundle.

Each:term:`environment` can override the default configuration by providing a

specific configuration file. For example, the ``dev`` environment loads the