repo_zf1/documentation/manual/en/module_specs/Zend_Application-TheoryOfOperation.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- Reviewed: no -->
<sect1 id="zend.application.theory-of-operation">
    <title>Theory of Operation</title>

    <para>
        Getting an <acronym>MVC</acronym> 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.
    </para>

    <para>
        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 <acronym>MVC</acronym> for a cronjob, or just the DB layer for a service script.
    </para>

    <para>
        <classname>Zend_Application</classname> aims to make this easier and to
        promote reuse by encapsulating bootstrapping into <acronym>OOP</acronym> paradigms.
    </para>

    <para>
        <classname>Zend_Application</classname> is broken into three realms:
    </para>

    <itemizedlist>
        <listitem>
            <para>
                <classname>Zend_Application</classname>: loads the <acronym>PHP</acronym>
                environment, including include_paths and autoloading, and instantiates
                the requested bootstrap class.
            </para>
        </listitem>

        <listitem>
            <para>
                <classname>Zend_Application_Bootstrap</classname>: provides
                interfaces for bootstrap classes.
                <classname>Zend_Application_Bootstrap_Bootstrap</classname> provides common
                functionality for most bootstrapping needs, including
                dependency checking algorithms and the ability to load
                bootstrap resources on demand.
            </para>
        </listitem>

        <listitem>
            <para>
                <classname>Zend_Application_Resource</classname> provides an
                interface for standard bootstrapping resources that can be
                loaded on demand by a bootstrap instance, as well as several
                default resource implementations.
            </para>
        </listitem>
    </itemizedlist>

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

    <itemizedlist>
        <listitem>
            <para>
                The current environment
            </para>
        </listitem>

        <listitem>
            <para>
                Options for bootstrapping
            </para>
        </listitem>
    </itemizedlist>

    <para>
        The bootstrap options include the path to the file containing the
        bootstrap class and optionally:
    </para>

    <itemizedlist>
        <listitem>
            <para>
                Any extra include_paths to set
            </para>
        </listitem>

        <listitem>
            <para>
                Any additional autoloader namespaces to register
            </para>
        </listitem>

        <listitem>
            <para>
                Any <filename>php.ini</filename> settings to initialize
            </para>
        </listitem>

        <listitem>
            <para>
                The class name for the bootstrap class (if not "Bootstrap")
            </para>
        </listitem>

        <listitem>
            <para>
                Resource prefix to path pairs to use
            </para>
        </listitem>

        <listitem>
            <para>
                Any resources to use (by class name or short name)
            </para>
        </listitem>

        <listitem>
            <para>
                Additional path to a configuration file to load
            </para>
        </listitem>

        <listitem>
            <para>
                Additional configuration options
            </para>
        </listitem>
    </itemizedlist>

    <para>
        Options may be an array, a <classname>Zend_Config</classname> object, or the path
        to a configuration file.
    </para>

    <sect2 id="zend.application.theory-of-operation.bootstrap">
        <title>Bootstrapping</title>

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

        <programlisting language="php"><![CDATA[
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();
}
]]></programlisting>

        <para>
            This <acronym>API</acronym> 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.
        </para>

        <para>
            You can implement this interface on your own, extend
            <classname>Zend_Application_Bootstrap_BootstrapAbstract</classname>, or use
            <classname>Zend_Application_Bootstrap_Bootstrap</classname>.
        </para>

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

        <sect3 id="zend.application.theory-of-operation.bootstrap.resource-methods">
            <title>Resource Methods</title>

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

            <para>
                To bootstrap a single resource method, use the
                <methodname>bootstrap()</methodname> method, and pass it the name of the
                resource. The name will be the method name minus the
                <emphasis>_init</emphasis> prefix.
            </para>

            <para>
                To bootstrap several resource methods, pass an array of names.
                Too bootstrap all resource methods, pass nothing.
            </para>

            <para>
                Take the following bootstrap class:
            </para>

            <programlisting language="php"><![CDATA[
class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    protected function _initFoo()
    {
        // ...
    }

    protected function _initBar()
    {
        // ...
    }

    protected function _initBaz()
    {
        // ...
    }
}
]]></programlisting>

            <para>
                To bootstrap just the <methodname>_initFoo()</methodname> method, do the
                following:
            </para>

            <programlisting language="php"><![CDATA[
$bootstrap->bootstrap('foo');
]]></programlisting>

            <para>
                To bootstrap the <methodname>_initFoo()</methodname> and
                <methodname>_initBar()</methodname> methods, do the following:
            </para>

            <programlisting language="php"><![CDATA[
$bootstrap->bootstrap(array('foo', 'bar'));
]]></programlisting>

            <para>
                To bootstrap all resource methods, call <methodname>bootstrap()</methodname>
                with no arguments:
            </para>

            <programlisting language="php"><![CDATA[
$bootstrap->bootstrap();
]]></programlisting>
        </sect3>

        <sect3 id="zend.application.theory-of-operation.bootstrap.resource-plugins">
            <title>Bootstraps that use resource plugins</title>

            <para>
                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 <link
                    linkend="zend.application.theory-of-operation.resources">how
                    to create resources</link> later; in
                this section we will show you how to utilize them only.
            </para>

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

        <programlisting language="php"><![CDATA[
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();
}
]]></programlisting>

            <para>
                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.
            </para>

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

            <para>
                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
                "<classname>Zend_Application_Resource_</classname>"; anything following this would
                be the name of the resource. As an example,
            </para>

            <programlisting language="php"><![CDATA[
$application = new Zend_Application(APPLICATION_ENV, array(
    'resources' => array(
        'FrontController' => array(
            'controllerDirectory' => APPLICATION_PATH . '/controllers',
        ),
    ),
));
]]></programlisting>

            <para>
                This indicates that the "FrontController" resource should be
                used, with the options specified.
            </para>

            <para>
                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 <classname>Zend_Loader_PluginLoader</classname>, so you will only
                need to indicate the common class prefix an path pairs.
            </para>

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

            <programlisting language="php"><![CDATA[
$application = new Zend_Application(APPLICATION_ENV, array(
    'pluginPaths' => array(
        'My_Resource' => APPLICATION_PATH . '/resources/',
    ),
    'resources' => array(
        'FrontController' => array(
            'controllerDirectory' => APPLICATION_PATH . '/controllers',
        ),
    ),
));
]]></programlisting>

            <para>
                You would now be able to use resources from that directory.
            </para>

            <para>
                Just like resource methods, you use the <methodname>bootstrap()</methodname>
                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.
            </para>

            <programlisting language="php"><![CDATA[
// Execute one:
$bootstrap->bootstrap('FrontController');

// Execute several:
$bootstrap->bootstrap(array('FrontController', 'Foo'));

// Execute all resource methods and plugins:
$bootstrap->bootstrap();
]]></programlisting>
        </sect3>

        <sect3 id="zend.application.theory-of-operation.bootstrap.registry">
            <title>Resource Registry</title>

            <para>
                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?
            </para>

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

            <para>
                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
                <classname>Zend_Registry</classname> is used, but you may also specify any
                other object you wish. The methods <methodname>setContainer()</methodname>
                and <methodname>getContainer()</methodname> may be used to manipulate the
                container itself. <methodname>getResource($resource)</methodname> can be
                used to fetch a given resource from the container, and
                <methodname>hasResource($resource)</methodname> to check if the resource has
                actually been registered.
            </para>

            <para>
                As an example, consider a basic view resource:
            </para>

            <programlisting language="php"><![CDATA[
class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
{
    protected function _initView()
    {
        $view = new Zend_View();
        // more initialization...

        return $view;
    }
}
]]></programlisting>

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

            <programlisting language="php"><![CDATA[
// 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;
}
]]></programlisting>

            <para>
                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. <classname>Zend_Application_Bootstrap_Bootstrap</classname>
                provides some convenience for this: during its
                <methodname>run()</methodname> execution, it registers itself as the front
                controller parameter "bootstrap", which allows you to fetch it
                from the router, dispatcher, plugins, and action controllers.
            </para>

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

            <programlisting language="php"><![CDATA[
class FooController extends Zend_Controller_Action
{
    public function init()
    {
        $bootstrap = $this->getInvokeArg('bootstrap');
        $view = $bootstrap->getResource('view');
        // ...
    }
}
]]></programlisting>
        </sect3>

        <sect3 id="zend.application.theory-of-operation.bootstrap.dependency-tracking">
            <title>Dependency Tracking</title>

            <para>
                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.
            </para>

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

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

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

            <para>
                In a resource method, such a call would look like this:
            </para>

            <programlisting language="php"><![CDATA[
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;
    }
}
]]></programlisting>
        </sect3>
    </sect2>

    <sect2 id="zend.application.theory-of-operation.resources">
        <title>Resource Plugins</title>

        <para>
            <link
                linkend="zend.application.theory-of-operation.bootstrap.resource-plugins">As noted
                previously</link>, 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.
        </para>

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

        <programlisting language="php"><![CDATA[
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();
}
]]></programlisting>

        <para>
            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.
        </para>

        <para>
            As an example, let's assume you have a common view intialization you
            use in your applications. You have a common doctype, <acronym>CSS</acronym> 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:
        </para>

        <programlisting language="php"><![CDATA[
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;
    }
}
]]></programlisting>

        <para>
            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.
        </para>
    </sect2>
</sect1>