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The Controller

Still here after the first two parts? You are already becoming a Symfony2 addict! Without further ado, discover what controllers can do for you.

Using Formats

Nowadays, a web application should be able to deliver more than just HTML pages. From XML for RSS feeds or Web Services, to JSON for Ajax requests, there are plenty of different formats to choose from. Supporting those formats in Symfony2 is straightforward. Tweak the route by adding a default value of xml for the _format variable:

// src/Acme/DemoBundle/Controller/DemoController.php
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Template;

// ...

/**
 * @Route("/hello/{name}", defaults={"_format"="xml"}, name="_demo_hello")
 * @Template()
 */
public function helloAction($name)
{
    return array('name' => $name);
}

By using the request format (as defined by the special _format variable), Symfony2 automatically selects the right template, here hello.xml.twig:

<!-- src/Acme/DemoBundle/Resources/views/Demo/hello.xml.twig -->
<hello>
    <name>{{ name }}</name>
</hello>

That's all there is to it. For standard formats, Symfony2 will also automatically choose the best Content-Type header for the response. If you want to support different formats for a single action, use the {_format} placeholder in the route path instead:

// src/Acme/DemoBundle/Controller/DemoController.php
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Template;

// ...

/**
 * @Route(
 *     "/hello/{name}.{_format}",
 *     defaults = { "_format" = "html" },
 *     requirements = { "_format" = "html|xml|json" },
 *     name = "_demo_hello"
 * )
 * @Template()
 */
public function helloAction($name)
{
    return array('name' => $name);
}

The controller will now match URLs like /demo/hello/Fabien.xml or /demo/hello/Fabien.json.

The requirements entry defines regular expressions that variables must match. In this example, if you try to request the /demo/hello/Fabien.js resource, you will get a 404 HTTP error, as it does not match the _format requirement.

Redirecting and Forwarding

If you want to redirect the user to another page, use the redirect() method:

return $this->redirect($this->generateUrl('_demo_hello', array('name' => 'Lucas')));

The generateUrl() is the same method as the path() function used in the templates. It takes the route name and an array of parameters as arguments and returns the associated friendly URL.

You can also internally forward the action to another using the forward() method:

return $this->forward('AcmeDemoBundle:Hello:fancy', array(
    'name'  => $name,
    'color' => 'green'
));

Displaying Error Pages

Errors will inevitably happen during the execution of every web application. In the case of 404 errors, Symfony includes a handy shortcut that you can use in your controllers:

throw $this->createNotFoundException();

For 500 errors, just throw a regular PHP exception inside the controller and Symfony will transform it into a proper 500 error page:

throw new \Exception('Something went wrong!');

Getting Information from the Request

Symfony automatically injects the Request object when the controller has an argument that's type hinted with Symfony\Component\HttpFoundation\Request:

use Symfony\Component\HttpFoundation\Request;

public function indexAction(Request $request)
{
    $request->isXmlHttpRequest(); // is it an Ajax request?

    $request->getPreferredLanguage(array('en', 'fr'));

    $request->query->get('page');   // get a $_GET parameter

    $request->request->get('page'); // get a $_POST parameter
}

In a template, you can also access the Request object via the app.request variable:

{{ app.request.query.get('page') }}

{{ app.request.parameter('page') }}

Persisting Data in the Session

Even if the HTTP protocol is stateless, Symfony2 provides a nice session object that represents the client (be it a real person using a browser, a bot, or a web service). Between two requests, Symfony2 stores the attributes in a cookie by using native PHP sessions.

Storing and retrieving information from the session can be easily achieved from any controller:

use Symfony\Component\HttpFoundation\Request;

public function indexAction(Request $request)
{
    $session = $this->request->getSession();

    // store an attribute for reuse during a later user request
    $session->set('foo', 'bar');

    // get the value of a session attribute
    $foo = $session->get('foo');

    // use a default value if the attribute doesn't exist
    $foo = $session->get('foo', 'default_value');
}

You can also store "flash messages" that will auto-delete after the next request. They are useful when you need to set a success message before redirecting the user to another page (which will then show the message):

// store a message for the very next request (in a controller)
$session->getFlashBag()->add('notice', 'Congratulations, your action succeeded!');

{# display the flash message in the template #}
<div>{{ app.session.flashbag.get('notice') }}</div>

Caching Resources

As soon as your website starts to generate more traffic, you will want to avoid generating the same resource again and again. Symfony2 uses HTTP cache headers to manage resources cache. For simple caching strategies, use the convenient @Cache() annotation:

use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Template;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Cache;

/**
 * @Route("/hello/{name}", name="_demo_hello")
 * @Template()
 * @Cache(maxage="86400")
 */
public function helloAction($name)
{
    return array('name' => $name);
}

In this example, the resource will be cached for a day (86400 seconds). Resource caching is managed by Symfony2 itself. But because caching is managed using standard HTTP cache headers, you can use Varnish or Squid without having to modify a single line of code in your application.

Final Thoughts

That's all there is to it, and I'm not even sure you'll have spent the full 10 minutes. You were briefly introduced to bundles in the first part, and all the features you've learned about so far are part of the core framework bundle. But thanks to bundles, everything in Symfony2 can be extended or replaced. That's the topic of the :doc:`next part of this tutorial<the_architecture>`.