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Theory of Operation - Zend_Application

Theory of Operation

Getting an MVC application configured and ready to dispatch has required an increasing amount of code as more features become available: setting up the database, configuring your view and view helpers, configuring your layouts, registering plugins, registering action helpers, and more.

Additionally, you will often want to reuse the same code to bootstrap your tests, a cronjob, or a service script. While it's possible to simply include your bootstrap script, oftentimes there are initializations that are environment specific – you may not need the MVC for a cronjob, or just the DB layer for a service script.

Zend_Application aims to make this easier and to promote reuse by encapsulating bootstrapping into OOP paradigms.

Zend_Application is broken into three realms:

Zend_Application: loads the PHP environment, including include_paths and autoloading, and instantiates the requested bootstrap class.
Zend_Application_Bootstrap: provides interfaces for bootstrap classes. Zend_Application_Bootstrap_Bootstrap provides common functionality for most bootstrapping needs, including dependency checking algorithms and the ability to load bootstrap resources on demand.
Zend_Application_Resource provides an interface for standard bootstrapping resources that can be loaded on demand by a bootstrap instance, as well as several default resource implementations.

Developers create a bootstrap class for their application, extending Zend_Application_Bootstrap_Bootstrap or implementing (minimally) Zend_Application_Bootstrap_Bootstrapper. The entry point (e.g., public/index.php) will load Zend_Application, and instantiate it by passing:

The current environment
Options for bootstrapping

The bootstrap options include the path to the file containing the bootstrap class and optionally:

Any extra include_paths to set
Any additional autoloader namespaces to register
Any php.ini settings to initialize
The class name for the bootstrap class (if not "Bootstrap")
Resource prefix to path pairs to use
Any resources to use (by class name or short name)
Additional path to a configuration file to load
Additional configuration options

Options may be an array, a Zend_Config object, or the path to a configuration file.

Bootstrapping

Zend_Application's second area of responsibility is executing the application bootstrap. Bootstraps minimally need to implement Zend_Application_Bootstrap_Bootstrapper, which defines the following API:

interface Zend_Application_Bootstrap_Bootstrapper
{
    public function __construct($application);
    public function setOptions(array $options);
    public function getApplication();
    public function getEnvironment();
    public function getClassResources();
    public function getClassResourceNames();
    public function bootstrap($resource = null);
    public function run();
}

This API allows the bootstrap to accept the environment and configuration from the application object, report the resources its responsible for bootstrapping, and then bootstrap and run the application.

You can implement this interface on your own, extend Zend_Application_Bootstrap_BootstrapAbstract, or use Zend_Application_Bootstrap_Bootstrap.

Besides this functionality, there are a number of other areas of concern you should familiarize yourself with.

Resource Methods

The Zend_Application_Bootstrap_BootstrapAbstract implementation provides a simple convention for defining class resource methods. Any protected method beginning with a name prefixed with _init will be considered a resource method.

To bootstrap a single resource method, use the bootstrap() method, and pass it the name of the resource. The name will be the method name minus the _init prefix.

To bootstrap several resource methods, pass an array of names. Too bootstrap all resource methods, pass nothing.

Take the following bootstrap class:

class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    protected function _initFoo()
    {
        // ...
    }
 
    protected function _initBar()
    {
        // ...
    }
 
    protected function _initBaz()
    {
        // ...
    }
}

To bootstrap just the _initFoo() method, do the following:

$bootstrap->bootstrap('foo');

To bootstrap the _initFoo() and _initBar() methods, do the following:

$bootstrap->bootstrap(array('foo', 'bar'));

To bootstrap all resource methods, call bootstrap() with no arguments:

$bootstrap->bootstrap();

Bootstraps that use resource plugins

To make your bootstraps more re-usable, we have provided the ability to push your resources into resource plugin classes. This allows you to mix and match resources simply via configuration. We will cover how to create resources later; in this section we will show you how to utilize them only.

If your bootstrap should be capable of using resource plugins, you will need to implement an additional interface, Zend_Application_Bootstrap_ResourceBootstrapper. This interface defines an API for locating, registering, and loading resource plugins:

interface Zend_Application_Bootstrap_ResourceBootstrapper
{
    public function registerPluginResource($resource, $options = null);
    public function unregisterPluginResource($resource);
    public function hasPluginResource($resource);
    public function getPluginResource($resource);
    public function getPluginResources();
    public function getPluginResourceNames();
    public function setPluginLoader(Zend_Loader_PluginLoader_Interface $loader);
    public function getPluginLoader();
}

Resource plugins basically provide the ability to create resource intializers that can be re-used between applications. This allows you to keep your actual bootstrap relatively clean, and to introduce new resources without needing to touch your bootstrap itself.

Zend_Application_Bootstrap_BootstrapAbstract (and Zend_Application_Bootstrap_Bootstrap by extension) implement this interface as well, allowing you to utilize resource plugins.

To utilize resource plugins, you must specify them in the options passed to the application object and/or bootstrap. These options may come from a configuration file, or be passed in manually. Options will be of key to options pairs, with the key representing the resource name. The resource name will be the segment following the class prefix. For example, the resources shipped with Zend Framework have the class prefix "Zend_Application_Resource_"; anything following this would be the name of the resource. As an example,

$application = new Zend_Application(APPLICATION_ENV, array(
    'resources' => array(
        'FrontController' => array(
            'controllerDirectory' => APPLICATION_PATH . '/controllers',
        ),
    ),
));

This indicates that the "FrontController" resource should be used, with the options specified.

If you begin writing your own resource plugins, or utilize third-party resource plugins, you will need to tell your bootstrap where to look for them. Internally, the bootstrap utilizes Zend_Loader_PluginLoader, so you will only need to indicate the common class prefix an path pairs.

As an example, let's assume you have custom resource plugins in APPLICATION_PATH/resources/ and that they share the common class prefix of My_Resource. You would then pass that information to the application object as follows:

$application = new Zend_Application(APPLICATION_ENV, array(
    'pluginPaths' => array(
        'My_Resource' => APPLICATION_PATH . '/resources/',
    ),
    'resources' => array(
        'FrontController' => array(
            'controllerDirectory' => APPLICATION_PATH . '/controllers',
        ),
    ),
));

You would now be able to use resources from that directory.

Just like resource methods, you use the bootstrap() method to execute resource plugins. Just like with resource methods, you can specify either a single resource plugin, multiple plugins (via an array), or all plugins. Additionally, you can mix and match to execute resource methods as well.

// Execute one:
$bootstrap->bootstrap('FrontController');
 
// Execute several:
$bootstrap->bootstrap(array('FrontController', 'Foo'));
 
// Execute all resource methods and plugins:
$bootstrap->bootstrap();

Resource Registry

Many, if not all, of your resource methods or plugins will initialize objects, and in many cases, these objects will be needed elsewhere in your application. How can you access them?

Zend_Application_Bootstrap_BootstrapAbstract provides a local registry for these objects. To store your objects in them, you simply return them from your resources.

For maximum flexibility, this registry is referred to as a "container" internally; its only requirements are that it is an object. Resources are then registered as properties named after the resource name. By default, an instance of Zend_Registry is used, but you may also specify any other object you wish. The methods setContainer() and getContainer() may be used to manipulate the container itself. getResource($resource) can be used to fetch a given resource from the container, and hasResource($resource) to check if the resource has actually been registered.

As an example, consider a basic view resource:

class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    protected function _initView()
    {
        $view = new Zend_View();
        // more initialization...
 
        return $view;
    }
}

You can then check for it and/or fetch it as follows:

// Using the has/getResource() pair:
if ($bootstrap->hasResource('view')) {
    $view = $bootstrap->getResource('view');
}
 
// Via the container:
$container = $bootstrap->getContainer();
if (isset($container->view)) {
    $view = $container->view;
}

Please note that the registry and also the container is not global. This means that you need access to the bootstrap in order to fetch resources. Zend_Application_Bootstrap_Bootstrap provides some convenience for this: during its run() execution, it registers itself as the front controller parameter "bootstrap", which allows you to fetch it from the router, dispatcher, plugins, and action controllers.

As an example, if you wanted access to the view resource from above within your action controller, you could do the following:

class FooController extends Zend_Controller_Action
{
    public function init()
    {
        $bootstrap = $this->getInvokeArg('bootstrap');
        $view = $bootstrap->getResource('view');
        // ...
    }
}

Dependency Tracking

In addition to executing resource methods and plugins, it's necessary to ensure that these are executed once and once only; these are meant to bootstrap an application, and executing multiple times can lead to resource overhead.

At the same time, some resources may depend on other resources being executed. To solve these two issues, Zend_Application_Bootstrap_BootstrapAbstract provides a simple, effective mechanism for dependency tracking.

As noted previously, all resources -- whether methods or plugins -- are bootstrapped by calling bootstrap($resource), where $resource is the name of a resource, an array of resources, or, left empty, indicates all resources should be run.

If a resource depends on another resource, it should call bootstrap() within its code to ensure that resource has been executed. Subsequent calls to it will then be ignored.

In a resource method, such a call would look like this:

class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    protected function _initRequest()
    {
        // Ensure the front controller is initialized
        $this->bootstrap('FrontController');
 
        // Retrieve the front controller from the bootstrap registry
        $front = $this->getResource('FrontController');
 
        $request = new Zend_Controller_Request_Http();
        $request->setBaseUrl('/foo');
        $front->setRequest($request);
 
        // Ensure the request is stored in the bootstrap registry
        return $request;
    }
}

Resource Plugins

As noted previously, a good way to create re-usable bootstrap resources and to offload much of your coding to discrete classes is to utilize resource plugins. While Zend Framework ships with a number of standard resource plugins, the intention is that developers should write their own to encapsulate their own initialization needs.

Resource plugins need only implement Zend_Application_Resource_Resource, or, more simply still, extend Zend_Application_Resource_ResourceAbstract. The basic interface is simply this:

interface Zend_Application_Resource_Resource
{
    public function __construct($options = null);
    public function setBootstrap(
        Zend_Application_Bootstrap_Bootstrapper $bootstrap
    );
    public function getBootstrap();
    public function setOptions(array $options);
    public function getOptions();
    public function init();
}

The interface defines simply that a resource plugin should accept options to the constructor, have mechanisms for setting and retrieving options, have mechanisms for setting and retrieving the bootstrap object, and an initialization method.

As an example, let's assume you have a common view intialization you use in your applications. You have a common doctype, CSS and JavaScript, and you want to be able to pass in a base document title via configuration. Such a resource plugin might look like this:

class My_Resource_View extends Zend_Application_Resource_ResourceAbstract
{
    protected $_view;
 
    public function init()
    {
        // Return view so bootstrap will store it in the registry
        return $this->getView();
    }
 
    public function getView()
    {
        if (null === $this->_view) {
            $options = $this->getOptions();
            $title   = '';
            if (array_key_exists('title', $options)) {
                $title = $options['title'];
                unset($options['title']);
            }
 
            $view = new Zend_View($options);
            $view->doctype('XHTML1_STRICT');
            $view->headTitle($title);
            $view->headLink()->appendStylesheet('/css/site.css');
            $view->headScript()->appendfile('/js/analytics.js');
 
            $viewRenderer =
                Zend_Controller_Action_HelperBroker::getStaticHelper(
                    'ViewRenderer'
                );
            $viewRenderer->setView($view);
 
            $this->_view = $view;
        }
        return $this->_view;
    }
}

As long as you register the prefix path for this resource plugin, you can then use it in your application. Even better, because it uses the plugin loader, you are effectively overriding the shipped "View" resource plugin, ensuring that your own is used instead.

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