ASP Tutorial: The Global.asa file - Complete Reference

The Global.asa file is an optional file that can contain declarations of objects, variables, and methods that can be accessed by every page in an ASP application.

The Global.asa file
The Global.asa file is an optional file that can contain declarations of objects, variables, and methods that can be accessed by every page in an ASP application. All valid browser scripts (JavaScript, VBScript, JScript, PerlScript, etc.) can be used within Global.asa.

The Global.asa file can contain only the following:

Application events
Session events
<object> declarations
TypeLibrary declarations
the #include directive

Note: The Global.asa file must be stored in the root directory of the ASP application, and each application can only have one Global.asa file.

Events in Global.asa
In Global.asa you can tell the application and session objects what to do when the application/session starts and what to do when the application/session ends. The code for this is placed in event handlers. The Global.asa file can contain four types of events:

Application_OnStart - This event occurs when the FIRST user calls the first page from an ASP application. This event occurs after the Web server is restarted or after the Global.asa file is edited. The "Session_OnStart" event occurs immediately after this event.

Session_OnStart - This event occurs EVERY time a NEW user requests his or her first page in the ASP application.

Session_OnEnd - This event occurs EVERY time a user ends a session. A user ends a session after a page has not been requested by the user for a specified time (by default this is 20 minutes).

Application_OnEnd - This event occurs after the LAST user has ended the session. Typically, this event occurs when a Web server stops. This procedure is used to clean up settings after the Application stops, like delete records or write information to text files.

A Global.asa file could look something like this:



Note: We cannot use the ASP script delimiters (<% and %>) to insert scripts in the Global.asa file, we will have to put the subroutines inside the HTML tag.

<object> Declarations
It is possible to create objects with session or application scope in Global.asa by using the <object> tag.
Note: The <object> tag should be outside the tag!

Syntax




Examples
The first example creates an object of session scope named "MyAd" by using the ProgID parameter:



The second example creates an object of application scope named "MyConnection" by using the ClassID parameter:



The objects declared in the Global.asa file can be used by any script in the application:

GLOBAL.ASA:

You could reference the object "MyAd" from any page in the ASP application:

SOME .ASP FILE:


TypeLibrary Declarations
A TypeLibrary is a container for the contents of a DLL file corresponding to a COM object. By including a call to the TypeLibrary in the Global.asa file, the constants
of the COM object can be accessed, and errors can be better reported by the ASP code. If your Web application relies on COM objects that have declared data types in type libraries, you can declare the type libraries in Global.asa.

Syntax




Error Values
The server can return one of the following error messages:



Note: METADATA tags can appear anywhere in the Global.asa file (both inside and outside    tags). However, it is recommended that METADATA tags appear near the top of the Global.asa file.

Restrictions
Restrictions on what you can include in the Global.asa file:

You can not display text that is written in the Global.asa file. This file cant display information. You can only use Server and Application objects in the Application_OnStart and Application_OnEnd subroutines. In the Session_OnEnd subroutine, you can use Server, Application, and Session objects. In the Session_OnStart subroutine you can use any built-in object

How to use the Subroutines
Global.asa is often used to initialize variables.
The example below shows how to detect the exact time a visitor first arrives on a Web site. The time is stored in a Session variable named "started", and the value of the "started" variable can be accessed from any ASP page in the application:



Global.asa can also be used to control page access.
The example below shows how to redirect every new visitor to another page, in this case to a page called "newpage.asp":



And you can include functions in the Global.asa file.
In the example below the Application_OnStart subroutine occurs when the Web server starts. Then the Application_OnStart subroutine calls another subroutine named "getcustomers". The "getcustomers" subroutine opens a database and retrieves a record set from the "customers" table. The record set is assigned to an array, where it can be accessed from any ASP page without querying the database:



Global.asa Example
In this example we will create a Global.asa file that counts the number of current visitors.

The Application_OnStart sets the Application variable "visitors" to 0 when the server starts.
The Session_OnStart subroutine adds one to the variable "visitors" every time a new visitor arrives.
The Session_OnEnd subroutine subtracts one from "visitors" each time this subroutine is triggered

The Global.asa file:


To display the number of current visitors in an ASP file:



source : w3schools.com