Note: If you have not already read Joomla! Execution Path Walkthrough, you may want to read it first.

The entry point into a Joomla! component is similar from component to component.  For this example, we will use the Web Links core component.  The first file to be executed in the front end is:

.../components/com_weblinks/weblinks.php

First we see the security check to make sure no one calls this page directly.  This is standard and should be in all your php files (although there are a few exceptions):

// no direct access

defined('_JEXEC') or die('Restricted access');

Next, we require (include) the controller.php class that is in the same directory:

// Require the base controller

require_once (JPATH_COMPONENT.DS.'controller.php');

We check the query string to see if a specific controller name was sent in.  If so, we make sure to require the required file in the controllers directory as well:

// Require specific controller if requested

if($controller = JRequest::getWord('controller')) {

	$path = JPATH_COMPONENT.DS.'controllers'.DS.$controller.'.php';

	if (file_exists($path)) {

		require_once $path;

	} else {

		$controller = '';

	}

}

We then create an instance of our controller using the name we set above:

// Create the controller

$classname = 'WeblinksController'.ucfirst($controller);

$controller = new $classname( );

And execute the task that was requested in the query string parameter:

// Perform the Request task

$controller->execute(JRequest::getCmd('task'));

Once the task is complete, we redirect if needed:

// Redirect if set by the controller

$controller->redirect();

Next, we open up the controller class.