Joomla execution path work-through

When debugging issues or doing development in Joomla!, it ishelpful to understand the basic Joomla! Execution Path.<wbr>The execution path is the list of function callsthat are made during each page request. <wbr>While thecalls will change from request to request (depending on querystring parameters, cookies, session information, etc), the basicpath is the same each time. <wbr>We will cover thebasics and provide information to help developers find informationfor their<wbr>specific<wbr>situation.</wbr></wbr></wbr></wbr></wbr>

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Almost all requests to Joomla! start with the index.php filefound in the root of the Joomla! installation.<wbr>Administrator requests go to the<strong>.../administrator/index.php</strong> file, but are similarto front-end calls. <wbr>There are also some caseswhere certain pages can be called directly, but in most cases,index.php is the starting point.</wbr></wbr>

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.../index.php

The following code is a security measure and defines a variableother pages use to make sure no one calls them directly.<wbr>All other php files that should not be calleddirectly in Joomla! should include a check for this variable at thetop of the file:</wbr>

// Set flag that this is a parent file
define( '_JEXEC', 1 );

We then setup some other variables and include/require somefiles. <wbr>The PROFILER code is used if you haveDebug System turned On in the Global Configuration and is used toprint out debug information at the bottom of the page.<wbr>We will see more calls like this throughout thefile and will ignore them:</wbr></wbr>

define('JPATH_BASE', dirname(__FILE__) );
define( 'DS', DIRECTORY_SEPARATOR );
require_once ( JPATH_BASE .DS.'includes'.DS.'defines.php' );
require_once ( JPATH_BASE .DS.'includes'.DS.'framework.php' );
JDEBUG ? $_PROFILER->mark( 'afterLoad' ) : null;

Finally, we do some work and get the Joomla! JApplication objectand call it's initialise method:

$mainframe =& JFactory::getApplication('site');

$mainframe->initialise();

The online Joomla! API site is a great place to use as areference for looking up functions. <wbr>ThegetApplication function and initialise method can be foundhere:</wbr>

http://api.joomla.org/Joomla-Framework/JFactory.html#getApplication

http://api.joomla.org/Joomla-Framework/Application/JApplication.html#initialise

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The API lists the files associated with these two classes whichcan be found here:

.../libraries/joomla/factory.php

.../libraries/joomla/application/application.php

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For now, we won't worry about the specifics of the JApplicationinitialise method. <wbr>If you want to open the fileand look at the code to see what it does, that is the best way tolearn. <wbr>For now, just know that it initialises theapplication. ;-)</wbr></wbr>

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Next, we import the system plugins and trigger theonAfterInitialise method on them:

JPluginHelper::importPlugin('system');
// trigger the onAfterInitialise events
JDEBUG ? $_PROFILER->mark('afterInitialise') : null;
$mainframe->triggerEvent('onAfterInitialise');

The triggerEvent method is another one that we will seefrequently but won't explain every time. <wbr>Thiscall tells Joomla! to go through each enabled plugin of a certaintype and call the event on it. <wbr>In this case, thisis calling the System plugin onAfterInitialise event.</wbr></wbr>

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Next, we call the route method:

$mainframe->route();

This is the description of what the route method does and is inthe application.php code:

function route()

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Then we authorize that the user is allowed to see this menuitem:

// authorization
$Itemid = JRequest::getInt( 'Itemid');
$mainframe->authorize($Itemid);

Once we know the user is allowed, we dispatch the request to theappropriate component:

$option = JRequest::getCmd('option');
$mainframe->dispatch($option);

The dispatch method is a very important call.<wbr>This is the entry point into the component thatis being requested. <wbr>Every request to Joomla! endsup going to a specific component and follows a similar path.<wbr>For this example, let's assume we are requestingthe following URL:</wbr></wbr></wbr>

/index.php?option=com_content&view=article&id=39&Itemid=37

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This is telling Joomla! to route the request to the com_contentcomponent. <wbr>The Itemid query string variable tellsJoomla! which menu item this request is for (as used above whenauthorizing). <wbr>Most of the other query stringvariables are used in the component, but a lot of them (view,controller, task, etc) are used across most components.</wbr></wbr>

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Joomla! will then execute the following file for thecomponent:

.../components/com_content/content.php

For a component named com_somethingelse, Joomla! wouldexecute:

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.../components/com_somethingelse/somethingelse.php

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To see a full explanation of the execution path once inside acomponent, see the article<wbr><a href="http://www.cmsmarket.com/resources/dev-corner/112-joomla-component-execution-path-walkthrough" target="_blank">Joomla! Component Execution PathWalkthrough</a>.</wbr>

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Finally, we render out the resulting response to the user:

$mainframe->render();

// trigger the onAfterRender events
JDEBUG ? $_PROFILER->mark('afterRender') : null;
$mainframe->triggerEvent('onAfterRender');

echo JResponse::toString($mainframe->getCfg('gzip'));

The render method is another very important call.<wbr>This call will tell the JDocument object torender itself and will result in the template and modules beingrendered. <wbr>This topic will also be covered inanother future article that will eventually be linked to fromhere.</wbr></wbr>

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And that is it. <wbr>Not terribly complicated andeasy to follow.</wbr>

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Other resources

PHP has wonderfully helpful functions called debug_backtrace anddebug_print_backtrace that will tell you the path PHP took to getto the code you are at:

http://php.net/manual/en/function.debug-backtrace.php

If you know you are getting to a certain place in the code butnot sure what path was taken, use these functions to help debug theissue.

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PHP also has a wonderful function called print_r.<wbr>While the print function can be used to print astring or number, it can't be used to easily print out an object.<wbr>That is where print_r can be helpful:</wbr></wbr>

http://php.net/manual/en/function.print-r.php