ASP. NET global. asax event

The global. asax file is sometimes called an ASP. NET application. Program File, provides a way to respond to application-level or module-level events at a central location. You can use this file to implement application security and other tasks. The following describes how to use this file in application development.

Overview
Global. asax is in the application root directory. Although Visual Studio. NET automatically inserts this file into all ASP. NET projects, it is actually an optional file. There is no problem with deleting it-of course you are not using it .. The asax file extension indicates that it is an application file, rather than an ASP. NET file that uses Aspx.
The global. asax file is configured as any direct HTTP Request (via URL) and is automatically rejected. Therefore, users cannot download or view its content. The ASP. NET page framework can automatically identify any changes made to the Global. asax file. After global. asax is changed, the ASP. NET page framework restarts the application, including closing all browser sessions, removing all status information, and restarting the application domain.

Programming
The global. asax file inherits from the httpapplication class. It maintains an httpapplication Object pool and assigns the objects in the pool to the application as needed. The global. asax file contains the following events:
Application_init: this event is triggered when an application is instantiated or called for the first time. All httpapplication object instances are called.
Application_disposed: triggered before the application is destroyed. This is an ideal location for clearing previously used resources.
Application_error: this event is triggered when an unhandled exception is encountered in the application.
Application_start: this event is triggered when the first instance of the httpapplication class is created. It allows you to create objects that can be accessed by all httpapplication instances.
Application_end: this event is triggered when the last instance of the httpapplication class is destroyed. It is triggered only once during the lifecycle of an application.
Application_beginrequest: triggered when an application request is received. A request is the first trigger event. A request is generally a page request (URL) entered by the user ).
Application_endrequest: the last event requested by the application.
Application_prerequesthandlerexecute: this event is triggered before the ASP. NET page framework starts to execute Event Handlers such as pages or web services.
Application_postrequesthandlerexecute: this event is triggered when the ASP. NET page framework finishes executing an event handler.
Applcation_presendrequestheaders: this event is triggered when the ASP. NET page framework sends an HTTP header to the requesting client (browser.
Application_presendcontent: this event is triggered when the ASP. NET page framework sends content to the requesting client (browser.
Application_acquirerequeststate: this event is triggered when the ASP. NET page framework obtains the current state (session state) related to the current request.
Application_releaserequeststate: this event is triggered when the ASP. NET page framework executes all event handlers. This causes all status modules to save their current status data.
Application_resolverequestcache: this event is triggered when the ASP. NET page framework completes an authorization request. It allows the cache module to provide services for requests from the cache, bypassing the execution of event handlers.
Application_updaterequestcache: When the ASP. NET page framework executes the event processing program, this event is triggered, so that the cache module stores response data for use in response to subsequent requests.
Application_authenticaterequest: this event is triggered when the security module establishes a valid identity for the current user. At this time, the user's creden。 will be verified.
Application_authorizerequest: this event is triggered when the security module confirms that a user can access the resource.
Session_start: this event is triggered when a new user accesses the Application Web site.

Session_end: this event is triggered when a user's session times out, ends, or they leave the Application Web site.
The application_error event displays a simple message to indicate an error.

This event list seems to be scary, but these events may be very useful in different environments. A key issue with using these events is to know the order in which they are triggered. The application_init and application_start events are triggered once when the application is started for the first time. Similarly, application_disposed and application_end events are triggered once upon application termination. In addition, session-based events (session_start and session_end) are only used when users enter and exit the site. Other events process application requests. These events are triggered in the following order:
Application_beginrequest
Application_authenticaterequest
Application_authorizerequest
Application_resolverequestcache
Application_acquirerequeststate
Application_prerequesthandlerexecute
Application_presendrequestheaders
Application_presendrequestcontent
<Execution Code >
Application_postrequesthandlerexecute
Application_releaserequeststate
Application_updaterequestcache
Application_endrequest

These events are often used for security.

 

From: http://www.cnblogs.com/chapchao/archive/2009/04/08/1432048.html