David raised an interesting question in his very first post on the Joomla! forums, about using jimport() for classes that are deeply nested in the framework’s directory structure. The answer is simple: don’t load those classes. Problem solved! Right ?
Well, right, but why can’t you load them?
What is jimport?
Joomla!’s framework is located in /libraries/joomla. Instead of using require_once to load those files, you use the jimport() function. It uses a syntax with dots: to load /libraries/joomla/utilities/utility.php, you write jimport(‘joomla.utilities.utility’); The JUtility class is now available for you to use in your code.
The same thing goes for files that are nested deeper, like /libraries/joomla/application/component/view.php:
In J!1.5RC4, jimport got a little smarter. When using PHP5, instead of loading the file right away, the filename and the classname are registered, and loading is deferred until the class is actually needed. So when looking at our first example:
(This may look a little unnecessary: why not load the file right away, if we’re going to need it anyway? For now, let me just say that there are a number of scenario’s where this is a good idea, like in legacy mode. We’ll deal with those in another blog post.)
So what’s happening? jimport looks at the last part of the ‘joomla.utilities.utility’ string, adds a ‘J’ prefix, and registers the resulting ‘JUtility’ as the class name for utility.php. When you use JUtility, in the example above, or in MyClass extends JUtility, or in class_exists(‘JUtility’), the file utility.php is loaded.
David wonders in his post what happens when you want to use JSessionStorageDatabase, located in /libraries/joomla/session/storage/database.php. According to what I wrote above, you need to use jimport(‘joomla.session.storage.database’). However, this would register JDatabase as the classname, but in fact it should be JSessionStorageDatabase. Trying to use the class results in an error, because the file containing it isn’t being loaded. In reality, we never need to load classes like JSessionStorageDatabase in our code. Joomla! has factories for that.
Your code doesn’t have to worry about how to instantiate certain objects. The specifics are all handled by JFactory and a bunch of getInstance methods. Eg. JFactory::getDBO() might give you a JDatabaseMySQL object or a JDatabaseMySQLi object, or perhaps even a JDatabasePostgresSQL object in a later version. JFactory::getSession() gives you a JSession object. This object contains a JSessionStorage object, which can be JSessionStorageDatabase or JSessionStorageApc or any other. The point is: you don’t need to worry about it. JFactory (and JSession::getInstance(), JDatabase::getInstance(), …) take care of all that.
The only classes you need to use jimport for are classes with a single name like JFoo, not classes like JFooBar. And most importantly, always look at JFactory first, to see if you can get what you need there.