Attention

This manual is no longer being maintained for TYPO3 versions 11.5 and above. The majority of the content has been migrated to the Extbase or Fluid sections in "TYPO3 Explained".

Creating Controllers and Actions

The Controller classes are stored in the folder EXT:sjr_offer/Classes/Controller/. The name of the Controller is composed by the name of the Domain Model and the Suffix Controller. So the Controller \MyVendor\SjrOffers\Controller\OfferController is assigned to the Aggregate Root Object \MyVendor\SjrOffers\Domain\Model\Offer. And the name of the Class file is OfferController.php.

The Controller class must extend the class \TYPO3\CMS\Extbase\Mvc\Controller\ActionController which is part of Extbase. The individual Actions are combined in separate methods. The method names have to end in Action. The body of OfferController thus looks like this:

OfferController.php
<?php

namespace MyVendor\SjrOffers\Controller;

use TYPO3\CMS\Extbase\Mvc\Controller\ActionController;

class OfferController extends ActionController
{
   // Action methods will be following here
}

When realizing the desired tasks through Action methods you will often stumble upon very similar flows and patterns. Each task will be carried out by a single Action or a chain of Actions:

  1. A list of Domain Objects is to be displayed.

  2. A single Domain Object is to be displayed.

  3. A new Domain Object is to be created.

  4. An existing Domain Object is to be edited.

  5. A Domain Object is to be deleted.

We will shed some light on these recurring patterns in the following sections. Together with the schedule model you will learn the background to generate your own flows.

Tip

Note that you are free to choose the method names for your Actions as you like. Nevertheless we recommend to stick to the names presented here, to help other developers to find their way through your code.

Flow Pattern "display a list of Domain Objects"

The first pattern in our example fits the action "display a list of all offers". One action method usually will be enough for implementing this. We choose indexAction as name of the method:

// …
/**
 * @var OfferRepository
 */
private $offerRepository;

/**
 * Inject the offer repository
 *
 * @param \MyVendor\SjrOffers\Domain\Repository\OfferRepository $offerRepository
 */
public function injectOfferRepository(OfferRepository $offerRepository)
{
   $this->offerRepository = $offerRepository;
}

/**
 * Index Action
 *
 * @return string
 */
public function indexAction()
{
    $offers = $this->offerRepository->findAll();
    $this->view->assign('offers', $offers);
    return $this->view->render();
}

This can be simplified even more. As described in chapter 4 in section "controlling the flow", it is not necessary to return the rendered content. Furthermore we avoid initializing the variable $offers, which we only use once. So we get:

/**
 * Index Action
 *
 * @return void
 */
public function indexAction()
{
    $this->view->assign('offers', $this->offerRepository->findAll());
}

initializeAction

In old TYPO3 Versions the initializeAction() was used to get the repository instance. Later we can use this action, to modify the Request, before the property mapper is executed or integrate JavaScript libraries.

The ActionController not only calls the method initializeAction(), which is executed before any Action in the Controller, but also a method in the Form of initialize*Foo*Action(), which is called only before the method *foo*Action().

Tip

The trick of implementing an empty method body in the super class, which is the "filled" in the subclass is called Template Pattern.

Flow Pattern "display a single Domain Object"

The second pattern is best put into action by a single method as well. We call it showAction(). In contrast to indexAction we have to to tell this method from outside which Domain Object is to be displayed. In our case, the offer to be shown is passed to the method as Argument:

/**
 * Show action
 *
 * @param \MyVendor\SjrOffers\Domain\Model\Offer $offer The offer to be shown
 * @return string The rendered HTML string
 */
public function showAction(\MyVendor\SjrOffers\Domain\Model\Offer $offer)
{
   $this->view->assign('offer', $offer);
}

Usually the display of a single Object is called by a link in the frontend. In our example extension it connects the list view by something like the following URL:

https://example.org/index.php?id=123&amp;tx_sjroffers_pi1[offer]=3&amp;tx_sjroffers_pi1[action]=show&amp;tx_sjroffers_pi1[controller]=Offer

Due to the 2 Arguments tx_sjroffers_pi1[controller]=Offer and tx_sjroffers_pi1[action]=show, the dispatcher of Extbase passes the request to the OfferController. In the request we find the information that the Action show is to be called. Before passing on the further processing to the method showAction(), the Controller tries to map the Arguments received by the URL on the arguments of the method. Extbase maps the arguments by their names. In our example Extbase detects, that the GET Argument tx_sjroffers_pi1[offer]=3 corresponds to the method argument $offer: showAction(\MyVendor\SjrOffers\Domain\Model\Offer *$offer*). The type of this Argument is fetched by Extbase from the method signature: showAction(*\MyVendor\SjrOffers\Domain\Model\Offer* $offer). In case this so called Type Hint should not be present, Extbase reads the type from the annotation written above the method: @param *\MyVendor\SjrOffers\Domain\Model\Offer* $offer.

After successful assigning, the value of the incoming argument has to be casted in the target type as well as checked for validity (read more about validation in chapter 9 in section "Validating Domain Objects"). In our case the incoming value is "3". Target type is the class \MyVendor\SjrOffers\Domain\Model\Offer. So Extbase interprets the incoming value as uid of the object to be created and sends a request to the Storage Backend to find an Object with this uid. If the object can be reconstructed fully valid it is passed to the method as argument. Inside of the method showAction() the newly created object is passed on to the view, which is taking care of the HTML output as usual.

Tip

Inside of the template you can access all properties of the Domain Object, including all existing child objects. Thus this Flow Pattern does not only cover single domain objects but, in the event, also a complex aggregate.

If an Argument is identified as invalid, the already implemented method errorAction() of ActionController is called instead of the method showAction(). The method then generates a message for the frontend user and passes the processing to the previous Action, in case it is given. The latter is especially useful with invalid form field input as you'll see in the following.

Flow Pattern "creating a new Domain Object"

For the third Flow Pattern, the one for creating a new Domain Object, two steps are required: First, a form for inputting the Domain Data has to be shown in Frontend. Second, a new Domain Object has to be created (using the incoming form data) and put in the appropriate Repository. We're going to implement these two steps in the methods newAction() `and :php:`createAction().

Tip

We already described these steps in chapter 3 in section "Alternative route: creating a new posting". We now shortly revise this Flow using our example extension and focus on some further aspects.

First the method newAction() is called by a Link in frontend with the following URL:

https://example.org/index.php?id=123&amp;tx_sjroffers_pi1[organization]=5&amp;tx_sjroffers_pi1[action]=new&amp;tx_sjroffers_pi1[controller]=Offer

Extbase instantiates the Organization `Object which is mapped to the Argument :php:`$organization, just as it was the case with the Offer object in the method showAction(). In the URL is no information (yet) though, which value the Argument $newOffer shall have. So the default value (=null) set in the method signature is used. With these Arguments, the controller passes the further processing to the method newAction().

<?php
declare(strict_types = 1);

namespace MyVendor\SjrOffers\Controller;

use TYPO3\CMS\Extbase\Annotation as Extbase;
use TYPO3\CMS\Extbase\Mvc\Controller\ActionController;

class OfferController extends ActionController
{
    // ...

    /**
     * @param \MyVendor\SjrOffers\Domain\Model\Organization $organization The organization
     * @param \MyVendor\SjrOffers\Domain\Model\Offer $offer The new offer object
     * @return string An HTML form for creating a new offer
     * @Extbase\IgnoreValidation("newOffer")
     */
    public function newAction(\MyVendor\SjrOffers\Domain\Model\Organization $organization, \MyVendor\SjrOffers\Domain\Model\Offer $newOffer = null)
    {
        $this->view->assign('organization', $organization);
        $this->view->assign('newOffer', $newOffer);
        $this->view->assign('regions', $this->regionRepository->findAll());
    }

    // ...
}

This action passes to the view in organization the Organization object, in newOffer null (to begin with) the and in region all Region Objects contained in the RegionRepository. The view creates the output of the form in frontend, using a template, which we focus on in chapter 8 in section "Template Creation by example". After the user filled in the data of the offer and submitted the form, the Method createAction() shall be called. It expects as Arguments an Organization Object and an Object of the class \MyVendor\SjrOffers\Domain\Model\Offer. Therefore Extbase instantiates the Object and "fills" its Properties with the appropriate Form data. If all Arguments are valid, the Action createAction() is called.

/**
 * @param \MyVendor\SjrOffers\Domain\Model\Organization $organization The organization the offer belongs to
 * @param \MyVendor\SjrOffers\Domain\Model\Offer $newOffer A fresh Offer object which has not yet been added to the repository
 * @return void
 */
public function createAction(\MyVendor\SjrOffers\Domain\Model\Organization $organization, \MyVendor\SjrOffers\Domain\Model\Offer $newOffer)
{
   $organization->addOffer($newOffer);
   $newOffer->setOrganization($organization);
   $this->redirect('show', 'Organization', NULL, ['organization' => $organization]);
}

The new offer is allocated to the organization and inversely the organization is allocated to the offer. Thanks to this allocation Extbase will cause the persistence of the new offer in the dispatcher before returning to TYPO3.

After creating the new offer, the appropriate organization is to be displayed with all of its offers. We therefore start a new request (request-response-cycle) by redirecting to showAction() of the OrganizationController using the Method redirect(). The actual organization is hereby passed on as an argument. Inside the ActionController you have the following Methods for redirecting to other Action controllers at your disposal:

redirect($actionName, $controllerName = NULL, $extensionName = NULL,
   array $arguments = NULL, $pageUid = NULL, $delay = 0, $statusCode = 303)
redirectToURI($uri, $delay = 0, $statusCode = 303)
forward($actionName, $controllerName = NULL, $extensionName = NULL,array $arguments = NULL)

Using the redirect() Method, you can start a new request-response-cycle on the spot, similar to clicking on a link: The given Action (specified in $actionName) of the appropriate controller (specified in $controllerName) in the given extension (specified in $extensionName) is called. If you did not specify a controller or extension, Extbase assumes, that you stay in the same context. In the fourth parameter $arguments you can pass an Array of arguments. In our example ['organization' => $organization] would look like this in the URL: tx_sjroffers_pi1[organization]=5. The Array key is transcribed to the parameter name, while the organization object in $organization is transformed into the number 5, which is the appropriate UID. If you want to link to another page inside the TYPO3 installation, you can pass its uid in the 5th parameter ($pageUid). A delay before redirecting can be achieved by using the 6th parameter ($delay). By default the reason for redirecting is set to status code 303 (which means See Other).You can use the 7th parameter ($statusCode) to override this (for example with 301, which means Moved Permanently).

In our example, the following code is sent to the Browser. It provokes the immediate reload of the page with the given URL:

<html><head><meta http-equiv="refresh" content="0;url=https://example.org/
index.php?id=123&amp;tx_sjroffers_pi1[organization]=5&amp;tx_sjroffers_
pi1[action]=show&amp;tx_sjroffers_pi1[controller]=Organization"/></head></html>

The Method redirectToURI() corresponds to the Method redirect(), but you can directly set a URL respectively URI as string, e.g. <html><head><meta http-equiv= "refresh" content="0;url=https://example.org/foo/bar.html"/></head></html>. With this, you have all the freedom to do what you need. The Method forward(), at last, does a redirect of the request to another Action on the spot, just as the two redirect Methods. In contrast to them, no request-response-cycle ist started, though. The request Object is only updated with the details concerning Action, Controller and Extension, and then passed back to the dispatcher for processing. The dispatcher then passes on the actual Request- and Response- Objects to the appropriate Controller. Here, too, applies: If no Controller or Extension is set, the actual context is kept.

This procedure can be done multiple times when calling a page. There is the risk, though, that the process runs into an infinite loop (A redirects to B, B redirects to A again). In this case, Extbase stops the processing after some steps.

There is another important difference to the redirect Methods. When redirecting using the Method forward(), new objects will not (yet) be persisted to database. This is not done until at the end of a request-response-cycle. Therefore no UID has yet been assigned to a new Object and the transcription to a URL parameter fails. You can manually trigger the action of persisting before you execute the redirection, by using $this->objectManager->get(PersistenceManager::class)->persistAll(), though.

When calling the Method createAction(), we already described the case of all Arguments being valid. But what happens, if a Frontend user inserts invalid data - or even manipulates the form to deliberately attack the website?

Tip

You find detailed information about validation and security in chapter 9

Fluid adds multiple hidden fields to the form generated by the Method newAction(). These contain information about the origin of the form (__referrer) as well as, in encrypted form (__trustedProperties), the structure of the form (shorted in the example below).

<input type="hidden" name="tx_sjroffers_list[__referrer][extensionName]"
    value="SjrOffers" />
<input type="hidden" name="tx_sjroffers_list[__referrer][controllerName]" value="Offer" />
<input type="hidden" name="tx_sjroffers_list[__referrer][actionName]" value="edit" />
<input type="hidden" name="tx_sjroffers_list[__trustedProperties]"
       value="a:4:{s:5:&quot;offer&quot;;a:12:
...
s:10:&quot;__identity&quot;;i:1;}s:12:&quot;organization&quot;;i:1;
s:6:&quot;action&quot;;i:1;s:10:&quot;controller&quot;;
i:1;}8888b05fbf35fc96d0e3aadd370a8856a9edad20" />

If now a validation error occurs when calling the Method createAction(), an error message is saved and the processing is passed back to the previous Action, including all already inserted form data. Extbase reads the necessary information from the hidden fields __referrer. In our case the Method newAction() is called again. In contrast to the first call, Extbase now tries to create an (invalid) Offer Object from the form data, and to pass it to the Method in $newOffer. Due to the annotation @Extbase\IgnoreValidation("newOffer") Extbase this time accepts the invalid object and displays the form once more. Formerly filled in data is put in the fields again and the previously saved error message is displayed if the template is intending so.

../_images/figure-7-1.png

Figure 7-1: Wrong input in the form of an offer leads to an error message (in this case a modal JavaScript window)

Tip

Standard error messages of Extbase are not yet localized in Version 1.2 (TYPO3 4.4). In section "Localize error messages" in chapter 8, we describe a possibility to translate them too, though.

Using the hidden field __trustedProperties, the Extbase property mapper compares the incoming property data with the one that are allowed. If the request contains data for non whitelisted properties, the property mapper throws an exception.

Using the \TYPO3\CMS\Extbase\Annotation\IgnoreValidation("parameterName") annotation, you tell Extbase that the argument is not to be validated. If the argument is an Object, the validation of its properties is also bypassed.

Flow Pattern "Editing an existing Domain Object"

The flow pattern we now present you, is quite similar to the previous one. We again need two action Methods, which this time we call editAction() and updateAction(). The Method editAction() provides the form for editing, while updateAction() updates the Object in the Repository. In contrast to newAction() it is not necessary to pass an organization to the Method editAction(). It is sufficient to pass the offer to be edited as an Argument.

<?php
declare(strict_types = 1);

namespace MyVendor\SjrOffers\Controller;

use TYPO3\CMS\Extbase\Annotation as Extbase;
use TYPO3\CMS\Extbase\Mvc\Controller\ActionController;

class OfferController extends ActionController
{
    // ...

    /**
     * @param \MyVendor\SjrOffers\Domain\Model\Offer $offer The existing, unmodified offer
     * @return string Form for editing the existing organization
     * @Extbase\IgnoreValidation("offer")
     */
    public function editAction(\MyVendor\SjrOffers\Domain\Model\Offer $offer)
    {
       $this->view->assign('offer', $offer);
       $this->view->assign('regions', $this->regionRepository->findAll());
    }

    // ...
}

Note once again the annotation @Extbase\IgnoreValidation("offer"). The Method updateAction() receives the changed offer and updates it in the repository. Afterwards a new request is started and the organization is shown with its updated offers.

/**
 * @param \MyVendor\SjrOffers\Domain\Model\Offer $offer The modified offer
 * @return void
 */
public function updateAction(\MyVendor\SjrOffers\Domain\Model\Offer $offer)
{
   $this->offerRepository->update($offer);
   $this->redirect('show', 'Organization', NULL, ['organization' => $offer->getOrganization()]);
}

Warning

Do not forget to explicitly update the changed Domain Object using update(). Extbase will not do this automatically for you, for doing so could lead to unexpected results. For example if you have to manipulate the incoming Domain Object inside your Action Method.

At this point we have to ask ourselves how to prevent unauthorized changes of our Domain data. The organization and offer data are not to be changed by all visitors after all. So an administrator is allocated to each organization, authorized to change the data of that organization. The administrator can change the contact data of the organization, create and delete offers and contact persons as well as edit existing offers. Securing against unauthorized access can be done on different levels:

  • On the level of TYPO3, access to the page and/or plugin is prohibited.

  • Inside the Action, it is checked, if access is authorized. In our case it has to be checked if the administrator of the organization is logged in.

  • In the template, links to Actions, to which the frontend user has no access are blinded out.

Of these three levels, only the first two offer reliable protection. We do not take a closer look on the first level in this book. You can find detailed information for setting up permissions in your TYPO3 system in the Core API. The second level, we are going to implement in all "critical" Actions. Let's look at an example with the Method updateAction().

use TYPO3\CMS\Core\Utility\GeneralUtility;
use \MyVendor\SjrOffers\Service\AccessControlService;

public function initializeAction()
{
   $this->accessControlService = GeneralUtility::makeInstance(AccessControlService::class);
}

public function updateAction(\MyVendor\SjrOffers\Domain\Model\Offer $offer)
{
   $administrator = $offer->getOrganization()->getAdministrator();
   if ($this->accessControlService->isLoggedIn($administrator)) {
      $this->offerRepository->update($offer);
   } else {
      $this->flashMessages->add('Please sign in.');
   }
   $this->redirect('show', 'Organization', NULL, ['organization' => $offer->getOrganization()]);
}

We ask a previously instantiated AccessControlService if the administrator of the organization responsible for the offer is logged in the frontend. If yes, we do update the offer. If no, an error message is generated, which is displayed in the subsequently called organization overview.

Extbase does not yet offer an API for access control. We therefore implement an AccessControlService on ourselves. The description of the class is to be found in the file EXT:sjr_offers/Classes/Service/AccessControlService.php.

<?php

namespace MyVendor\SjrOffers\Service;

use TYPO3\CMS\Core\SingletonInterface;

class AccessControlService implements SingletonInterface
{

   public function isLoggedIn($person = NULL)
   {
      if (is_object($person)) {
         if ($person->getUid() === $this->getFrontendUserUid()) {
             return TRUE;
         }
      }
      return FALSE;
   }

   public function getFrontendUserUid()
   {
      if($this->hasLoggedInFrontendUser() && !empty($GLOBALS['TSFE']->fe_user->
             user['uid'])) {
         return intval($GLOBALS['TSFE']->fe_user->user['uid']);
      }
      return NULL;
   }

   public function hasLoggedInFrontendUser()
   {
      return $GLOBALS['TSFE']->loginUser === 1 ? TRUE : FALSE;
   }

}

The third level can easily be bypassed by manually typing the link or the form data. It therefore only reduces the confusion for honest visitors and the stimulus for the bad ones. Let's take a short look on this snippet from a template:

{namespace sjr=MyVendor\SjrOffers\ViewHelpers}
<!-- ... -->
<sjr:security.ifAuthenticated person="{organization.administrator}">
   <f:link.action controller="Offer" action="edit" arguments="{...}">
      <f:image src="EXT:sjr_offers/Resources/Public/Icons/edit.gif" alt="edit" />
   </f:link.action>
   <!-- ... -->
</sjr:security.ifAuthenticated>

Tip

A Service is often used to implement functionalities that are needed on multiple places in your extensions and are not related to one Domain Object.

Services are often stateless. In this context that means that their function does not depend on previous access. This does not rule out dependency to the "environment". In our example you can be sure, that a verification by isLoggedIn() always leads to the same result, regardless of any earlier verification - given that the "environment" has not changed (considerably), e.g. by the Administrator logging out or even losing his access rights.

Services usually can be built as Singleton (implements t3lib_Singleton). You can find detailed information to Singleton in chapter 2 in section "Singleton".

The AccessControlService is not Part of the Domain of our extension. It "belongs" to the Domain of the Content Management System. There are Domain Services also of course, like a Service creating a continuous invoice number. They are usually located in EXT:my_ext/Classes/Domain/Service/.

We make use of an IfAuthenticatedViewHelper to access the AccessControlService. The class file IfAuthenticatedViewHelper.php is in our case located in EXT:sjr_offers/Classes/ViewHelpers/Security/.

namespace MyVendor\SjrOffers\ViewHelper\Security;

use MyVendor\SjrOffers\Service\AccessControlService;
use TYPO3Fluid\Fluid\ViewHelpers\IfViewHelper;
use TYPO3\CMS\Core\Utility\GeneralUtility;

class IfAuthenticatedViewHelper extends IfViewHelper
{
   /**
    * @param mixed $person The person to be tested for login
    * @return string The output
    */
   public function render($person = NULL)
   {
      $accessControlService = GeneralUtility::makeInstance(AccessControlService::class);
      if ($accessControlService->isLoggedIn($person)) {
         return $this->renderThenChild();
      } else {
         return $this->renderElseChild();
      }
   }

}

The IfAuthenticatedViewHelper extends the If-ViewHelper of fluid and therefore provides the opportunity to use if-else branches. It delegates the access check to the AccessControlService. If the check gives a positive result, in our case a link with an edit icon is generated, which leads to the method editAction() of the OfferController.

Flow Pattern "Deleting a Domain Object"

The last Flow pattern realizes the deletion of an existing Domain Object in one single Action. The appropriate Method deleteAction() is kind of straightforward:

/**
 * @param \MyVendor\SjrOffers\Domain\Model\Offer $offer The offer to be deleted
 * @return void
 */
public function deleteAction(\MyVendor\SjrOffers\Domain\Model\Offer $offer)
{
   $administrator = $offer->getOrganization()->getAdministrator();
   if ($this->accessControlService->isLoggedIn($administrator)) {
      $this->offerRepository->remove($offer);
   } else {
      $this->flashMessages->add('Please sign in.');
   }
   $this->redirect('show', 'Organization', NULL, ['organization' => $offer->getOrganization()]);
}

The important thing here is that you delete the given Offer from the Repository using the method remove(). After running through your extension, Extbase will delete the associated record from the Database by marking it as deleted.

Tip

In principle it doesn't matter how you generate the result (usually HTML code) inside the Action. You can even decide to use the traditional way of building extensions in your Action - with SQL Queries and maker-based Templating. We invite you to pursue the path we chose up till now, though.

The flow patterns we present here are meant to be blueprints for your own flows. In real life projects they may get way more complex. The Method indexAction() of the OfferController looks like this in it's "final stage":

/**
 * @param \MyVendor\SjrOffers\Domain\Model\Demand $demand A demand (filter)
 * @return string The rendered HTML string
 */
public function indexAction(\MyVendor\SjrOffers\Domain\Model\Demand $demand = NULL)
{
   $allowedStates = (strlen($this->settings['allowedStates']) > 0) ?
         t3lib_div::intExplode(',', $this->settings['allowedStates']) : [];
   $listCategories = (strlen($this->settings['listCategories']) > 0) ?
         t3lib_div::intExplode(',', $this->settings['listCategories']) : [];
   $selectableCategories = (strlen($this->settings['selectableCategories']) > 0) ?
         t3lib_div::intExplode(',', $this->settings['selectableCategories']) : [];
   $propertiesToSearch = (strlen($this->settings['propertiesToSearch']) > 0) ?
         t3lib_div::trimExplode(',', $this->settings['propertiesToSearch']) : [];

   $this->view->assign('offers',
      $this->offerRepository->findDemanded(
         $demand,
         $propertiesToSearch,
         $listCategories,
         $allowedStates
      )
   );
   $this->view->assign('demand', $demand);
   $this->view->assign('organizations',
      array_merge(
         [0 => 'All Organisations'],
         $this->organizationRepository->findByStates($allowedStates)
      )
   );
   $this->view->assign('categories',
      array_merge(
         [0 => 'All Categories'],
         $this->categoryRepository->findSelectableCategories($selectableCategories)
      )
   );
   $this->view->assign('regions',
      array_merge(
         [0 => 'All Districts'],
         $this->regionRepository->findAll()
      )
   );
}

In the first few lines of the script, configuration options, set in the TypoScript template as comma separated list, are transcribed to arrays. Then this information is passed to the View piece by piece.

One requirement our extension has to realize, is that a visitor of the website can define a special demand, which is then used to filter the range of offers. We already implemented an appropriate Method findDemanded() (see chapter 6). To define his demand, the visitor chooses the accordant options in a form (see pic. 7-2).

../_images/figure-7-2.png

Figure 7-2: The buildup of the "demand" in a form above the offer list.

Warning

Watch out, that you do not implement logic, which actually belongs in the domain, inside of the Controller. Concentrate on the mere Flow.

Tip

In real life you will often need similar functionality in some or even all Controllers. The previously mentioned access control is a simple example. In our example extension we sourced it out to a service object. Another possibility is to create a basis Controller which extends the ActionController of Extbase. Inside you implement the shared functionality. Then the concrete controllers with your Actions extend this Basis Controller again.

The Flow inside of a Controller is triggered from outside by TYPO3. For extensions which generate content for the frontend, this is usually done by a plugin, placed on the appropriate page. How to configure such a plugin you'll see in the following section.