The application object encapsulates the execution context within which a request is
processed. Its main task is to collect some basic information about the request,
and dispatch it to an appropriate controller for further processing. It also serves
as the central place for keeping application-level configuration settings. For this
reason, the application object is also called the
By default, the application object is an instance of CWebApplication. To customize it, we normally provide a configuration settings file (or array) to initialize its property values when it is being instantiated. An alternative way of customizing it is to extend CWebApplication.
The configuration is an array of key-value pairs. Each key represents the name of a property of the application instance, and each value the corresponding property's initial value. For example, the following configuration array sets the name and defaultController properties of the application.
Note that application is a component like almost every Yii class. It means two things:
We usually store the configuration in a separate PHP script (e.g.
protected/config/main.php). Inside the script, we return the
configuration array as follows:
To apply the configuration, we pass the configuration file name as a parameter to the application's constructor, or to Yii::createWebApplication() in the following manner, usually in the entry script:
Tip: If the application configuration is very complex, we can split it into several files, each returning a portion of the configuration array. Then, in the main configuration file, we can call PHP
include()to include the rest of the configuration files and merge them into a complete configuration array.
The application base directory is the root directory under which all
security-sensitive PHP scripts and data reside. By default, it is a subdirectory
protected that is located under the directory containing the entry
script. It can be customized by setting the basePath
property in the application configuration.
Contents under the application base directory should be protected against being
accessed by Web users. With Apache HTTP server,
this can be done easily by placing an
.htaccess file under the base directory.
The content of the
.htaccess file would be as follows:
deny from all
The functionality of the application object can easily be customized and enriched using its flexible component architecture. The object manages a set of application components, each implementing specific features. For example, it performs some initial processing of a user request with the help of the CUrlManager and CHttpRequest components.
By configuring the components property of the application instance, we can customize the class and property values of any application component used. For example, we can configure the CMemCache component so that it can use multiple memcache servers for caching, like this:
array('host'=>'server1', 'port'=>11211, 'weight'=>60),
array('host'=>'server2', 'port'=>11211, 'weight'=>40),
To access an application component, use
ComponentID refers to the ID of the component (e.g.
An application component may be disabled by setting
enabled to false
in its configuration. Null is returned when we access a disabled component.
Tip: By default, application components are created on demand. This means an application component may not be created at all if it is not accessed during a user request. As a result, the overall performance may not be degraded even if an application is configured with many components. Some application components (e.g. CLogRouter) may need to be created regardless of whether they are accessed or not. To do so, list their IDs in the preload application property.
Yii predefines a set of core application components to provide features common among Web applications. For example, the request component is used to collect information about a user request and provide information such as the requested URL and cookies. By configuring the properties of these core components, we can change the default behavior of nearly every aspect of Yii.
Here is a list the core components that are pre-declared by CWebApplication:
When handling a user request, an application will undergo the following life cycle:
Pre-initialize the application with CApplication::preinit();
Set up the error handling;
Register core application components;
Load application configuration;
Initialize the application with CApplication::init()
Raise an onBeginRequest event;
Process the user request:
Raise an onEndRequest event;
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