Application|session| Object Author: scholar
In the previous article, the author gave you a detailed introduction of the ASP built-in object Response use method, in this article, the author will continue to introduce another two very useful and important ASP's built-in object application and session. In addition to the objects used to send, receive, and process data in an ASP's built-in objects, there are some very useful objects that represent Active Server applications and individual user information. Let's take a look at the Application object first. All. asp files in the same virtual directory and its subdirectories make up the ASP application. Instead of using the Application object, we can share information between all users of a given application and persist the data during the server's run. Also, the Application object has control over how the application-tier data is accessed and the events that can be used to trigger the process when the application starts and stops.
Now let's learn application objects together.
Properties Although a Pplication object has no built-in properties, we can use the following syntax to set a user-defined property, also known as a collection.
A pplication ("Attribute/collection name") = value
We can declare and establish the properties of the Application object using the following script. <% Application ("MyVar") = "Hello" Set Application ("myobj") = Server.CreateObject ("MyComponent")%> once we have assigned a PP Lication the object's properties, it will persist until the W-EB Server service is turned off so that A pplication stops. Because the values stored in a Pplication object can be read by all users of the application, the properties of a Pplication object are particularly suitable for passing information between users of the application.
Two, the method Application object has two methods, which are used to handle the problem that multiple users write to the data stored in application
1. The L Ock method prohibits other customers from modifying the properties of a Pplication object.
The Lock method prevents other customers from modifying variables stored in the Application object to ensure that only one customer can modify and access the application variable at the same time. If the user does not explicitly call the Unlock method, the server will unlock the Application object after the. asp file finishes or times out.
Let's take a look at the following program that uses a pplication to record page hits: < Dim numvisitsnumvisits=0 application.lockapplication ("numvisits") = Applic ation ("NumVisits") + 1 Application.UnLock%> Welcome to this page, you are the <%= application ("NumVisits")%> visitors! By saving the above script in your. asp file, you can easily add a counter to your page.
2, in contrast to the Lock method, the Unlock method allows other customers to modify the properties of the Application object.
In the above example, the Unlock method unlocks the object so that the next client can increase the value of the numvisits.
III. Events
1, Application_OnStart
A Pplication_onstart event occurs before the first time a new session (that is, the S Ession_onstart event) is created. A Pplication_onstart event is triggered when the W EB server is started and allows requests for files contained in the application. The process of a Pplication_onstart event must be written in the G Lobal.asa file. The syntax for the Application_OnStart event is as follows: < SCRIPT language=scriptlanguage runat=server> Sub Application_OnStart ... End Sub </script> 2, Application_OnEnd Application_OnEnd event occurs after the application exits after the Session_OnEnd event, Application_OnEnd event Process must also be written in the Global.asa file.
Let's take a look at some of the things you need to be aware of when using application objects.
You cannot store the A-SP built-in object in a Pplication object. For example, each of the following lines returns an error. <% Set Application ("Var1") =session Set Application ("Var2") =request Set Application ("Var3") =response set Application ("VAR4") =server Set Application ("VAR5") =application Set Application ("VAR6") =objectcontext%> If you store an array in the Application object, do not directly change the elements stored in the array. For example, the following script cannot be run. <% Application ("StoredArray") (3) = "New Value"%> this is because a Pplication object is implemented as a set. The array element S Toredarray (3) did not get a new assignment. This value will be included in the A Pplication object collection and will overwrite any information previously stored at this location. It is recommended that you get a copy of an array before retrieving or altering an object in an array when you store the array in a Pplication object. In an array operation, you should store all of the arrays in a Pplication object, so that any changes you make will be stored. This is demonstrated by the following script. ---asp8a.asp---<% Dim myarray () Redim myarray (5) myarray (0) = "Hello" myarray (1) = "Some other string" Application.Lock A Pplication ("StoredArray") =myarray application.unlock Response.Redirect "asp8b.asp"%>---asp8b.asp---<% Localarray=application ("StoredArray") localarray (1) = "There" Response.Write LocalArray (0) &localarray (1) Application.Lock Application ("StoredarRay ") =localarray Application.UnLock%> is a very useful ASP built-in object that has a similar effect to the Application object is the session. We can use the session object to store the information that is required for a particular user conversation. When a user jumps between pages of an application, the variables stored in the Session object are not purged, and the variables always exist when the user accesses the page in the application. When a user requests a Web page from an application, the Web server automatically creates a Session object if the user does not have a conversation. When a session expires or is discarded, the server terminates the session. You can manage the session object on the server by sending a unique Cookie to the client program. When a user requests a page in an ASP application for the first time, the ASP checks the HTTP header information to see if a Cookie named ASPSessionID in the message is sent, and if so, the server starts a new session and generates a globally unique value for the session. This value is sent to the client as the value of the new ASPSessionID cookie, which is used to access information that is stored on the server that is part of the client program. The most common function of the session object is to store user preferences. For example, if a user indicates that they don't like to view a graphic, they can store that information in the session object. In addition, it is often used in the process of identifying customer identities. Note that session state is reserved only in browsers that support cookies, and sessions will not work if the customer turns off the cookie option.
One, property
1, SessionID
The SessionID property returns the user's session identity. When you create a session, the server generates a separate identity for each session. The session identity is returned with a long shaping data type. In many cases SessionID can be used for WEB page registration statistics.
2. The TimeOut TimeOut property specifies the time-out period for the session object of the application in minutes. If you use
