In Symfony2, a tool named `Composer`_ handles this process.

The idea behind the autoloader is simple: the name of your class (including

the namespace) must match up with the path to the file containing that class.

Take the``FrameworkExtraBundle`` from the Symfony2 Standard Edition as an

Take the FrameworkExtraBundle from the Symfony2 Standard Edition as an

example::

The file itself lives at

``vendor/sensio/framework-extra-bundle/Sensio/Bundle/FrameworkExtraBundle/SensioFrameworkExtraBundle.php``.

As you can see, the location of the file follows the namespace of the class.

Specifically, the namespace, ``Sensio\Bundle\FrameworkExtraBundle``, spells out

the directory that the file should live in

As you can see, the second part of the path follows the namespace of the

class. The first part is equal to the package name of the SensioFrameworkExtraBundle.

The namespace, ``Sensio\Bundle\FrameworkExtraBundle``, and package name,

``sensio/framework-extra-bundle``, spells out the directory that the file

should live in

(``vendor/sensio/framework-extra-bundle/Sensio/Bundle/FrameworkExtraBundle/``).

Composer can then look for the file at this specific place and load it very fast.

Composer can then look for the file at this specific place and load it very

fast.

If the file did *not* live at this exact location, you'd receive a

``Class "Sensio\Bundle\FrameworkExtraBundle\SensioFrameworkExtraBundle" does not exist.``

error. In Symfony2, a "class does not exist" means that thesuspect class

namespace and physical location do not match. Basically, Symfony2 is looking

error. In Symfony2, a "class does not exist"errormeans that thenamespace of

the class and physical location do not match. Basically, Symfony2 is looking

in one exact location for that class, but that location doesn't exist (or

contains a different class). In order for a class to be autoloaded, you

**never need to clear your cache** in Symfony2.

As mentioned before, for the autoloader to work, it needs to know that the

``Sensio`` namespace lives in the ``vendor/bundles`` directory and that, for

example, the ``Doctrine`` namespace lives in the ``vendor/doctrine/orm/lib/``

directory. This mapping is entirely controlled by Composer. Each

third-party library you load throughcomposer has their settings defined

and Composer takes care of everything for you.

``Sensio`` namespace lives in the ``vendor/sensio/framework-extra-bundle``

directory and that, forexample, the ``Doctrine`` namespace lives in the

``vendor/doctrine/orm/lib/``directory. This mapping is entirely controlled by

Composer. Eachthird-party library you load throughComposer has their

settings definedand Composer takes care of everything for you.

For this to work, all third-party libraries used by your project must be

defined in the ``composer.json`` file.

If you look at the ``HelloController`` from the Symfony2 Standard Edition you

can see that it lives in the ``Acme\DemoBundle\Controller`` namespace. Yet, the

``AcmeDemoBundle`` is not defined in your ``composer.json`` file. Nonetheless are

the files autoloaded. This is because you can tellcomposer to autoload files

the files autoloaded. This is because you can tellComposer to autoload files

from specific directories without defining a dependency:

..code-block::yaml

This means that if a class is not found in the ``vendor`` directory, Composer

will search in the ``src`` directory before throwing a "class does not exists"

exception. Read more about configuring the Composer Autoloader in

`the Composer documentation`_

Using the Console

.. _`Composer`:http://getcomposer.org

.. _`Symfony2 Standard Edition`:https://github.com/symfony/symfony-standard

.. _`the Composer documentation`:http://getcomposer.org/doc/04-schema.md#autoload