30.1. Loading Files and Classes Dynamically

The Zend_Loader class includes methods to help you load files dynamically.

[Tip] Zend_Loader vs. require_once()

The Zend_Loader methods are best used if the filename you need to load is variable. For example, if it is based on a parameter from user input or method argument. If you are loading a file or a class whose name is constant, there is no benefit to using Zend_Loader over using traditional PHP functions such as require_once().

30.1.1. Loading Files

The static method Zend_Loader::loadFile() loads a PHP file. The file loaded may contain any PHP code. The method is a wrapper for the PHP function include(). This method returns boolean false on failure, for example if the specified file does not exist.

Example 30.1. Example of the loadFile() Method

Zend_Loader::loadFile($filename, $dirs=null, $once=false);

The $filename argument specifies the filename to load, which must not contain any path information. A security check is performed on $filename. The $filename may only contain alphanumeric characters, dashes ("-"), underscores ("_"), or periods ("."). No such restriction is placed on the $dirs argument.

The $dirs argument specifies which directories to search for the file in. If the value is NULL, only the include_path is searched; if the value is a string or an array, the directory or directories specified will be searched, followed by the include_path.

The $once argument is a boolean. If TRUE, Zend_Loader::loadFile() uses the PHP function include_once() for loading the file, otherwise the PHP function include() is used.

30.1.2. Loading Classes

The static method Zend_Loader::loadClass($class, $dirs) loads a PHP file and then checks for the existence of the class.

Example 30.2. Example of the loadClass() Method

Zend_Loader::loadClass('Container_Tree',
    array(
        '/home/production/mylib',
        '/home/production/myapp'
    )
);

The string specifying the class is converted to a relative path by substituting underscores with directory separators for your OS, and appending '.php'. In the example above, 'Container_Tree' becomes 'Container\\Tree.php' on Windows.

If $dirs is a string or an array, Zend_Loader::loadClass() searches the directories in the order supplied. The first matching file is loaded. If the file does not exist in the specified $dirs, then the include_path for the PHP environment is searched.

If the file is not found or the class does not exist after the load, Zend_Loader::loadClass() throws a Zend_Exception.

Zend_Loader::loadFile() is used for loading, so the class name may only contain alphanumeric characters and the hyphen ('-'), underscore ('_'), and period ('.').

30.1.3. Testing if a File is Readable

The static method Zend_Loader::isReadable($pathname) returns TRUE if a file at the specified pathname exists and is readable, FALSE otherwise.

Example 30.3. Example of isReadable() method

if (Zend_Loader::isReadable($filename)) {
    // do something with $filename
}

The $filename argument specifies the filename to check. This may contain path information. This method is a wrapper for the PHP function is_readable(). The PHP function does not search the include_path, while Zend_Loader::isReadable() does.

30.1.4. Using the Autoloader

The Zend_Loader class contains a method you can register with the PHP SPL autoloader. Zend_Loader::autoload() is the callback method. As a convenience, Zend_Loader provides the registerAutoload() function to register its autoload() method. If the spl_autoload extension is not present in your PHP environment, then the registerAutoload() method throws a Zend_Exception.

Example 30.4. Example of registering the autoloader callback method

Zend_Loader::registerAutoload();

After registering the Zend Framework autoload callback, you can reference classes from Zend Framework without having to load them explicitly. The autoload() method uses Zend_Loader::loadClass() automatically when you reference a class.

If you have extended the Zend_Loader class, you can give an optional argument to registerAutoload(), to specify the class from which to register an autoload() method.

Example 30.5. Example of registering the autoload callback method from an extended class

Because of the semantics of static function references in PHP, you must implement code for both loadClass() and autoload(), and the autoload() must call self::loadClass(). If your autoload() method delegates to its parent to call self::loadClass(), then it calls the method of that name in the parent class, not the subclass.

class My_Loader extends Zend_Loader
{
    public static function loadClass($class, $dirs = null)
    {
        parent::loadClass($class, $dirs);
    }

    public static function autoload($class)
    {
        try {
            self::loadClass($class);
            return $class;
        } catch (Exception $e) {
            return false;
        }
    }
}

Zend_Loader::registerAutoload('My_Loader');

You can remove an autoload callback. The registerAutoload() has an optional second argument, which is TRUE by default. If this argument is FALSE, the autoload callback is unregistered from the SPL autoload stack.

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