The Global.asax file, also known as the ASP.NET application file, is an optional file that contains code for responding to application-level events raised by ASP.NET or by HttpModules. The Global.asax file resides in the root directory of an ASP.NET-based application.
The Global.asax file is parsed and compiled into a dynamically generated .NET Framework class derived from the HttpApplication base class. The Global.asax file can contain application-level event handlers.
Example:
The following example shows a Global.asax file with an Application_Start event handler. The Application_Start event handler is called when a new user visits the application for the first time.
void Application_Start(object sender, EventArgs e)
{
// Code that runs on application startup
// Create a new database connection
string connectionString = “data source=localhost;initial catalog=MyDatabase;Integrated Security=SSPI;”;
SqlConnection myConnection = new SqlConnection(connectionString);
// Open the connection
myConnection.Open();
}