Asp Material 2

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Part – II A

popular

Working with Object buzzword

in

programming

is

“Object-Oriented

Programming”. OOP can help you in your ASP programming.

The Building Block of Objects Programming objects are composed of the things that describe them and the things that can be done with them. An object is something

that

typically

has

methods,

properties

or

collections. 

Properties

The things you can do with an object are called properties. Properties describe an object. An object’s properties can be read or set to specify the state of the object. 

Methods

An object’s methods determine the things that one can do with the object. Method associated with programming objects may also need information. They receive it in much the same way as the function and subroutines receive arguments. Methods often affect the values of the properties methods are also often used to retrieve the value of properties. Methods can also tell you the value of properties. 

Collections

An object’s collection is of Key and value pairs. Each page number (the Key) has a corresponding page of text (the value). 

Instances of Objects

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Jatin Soni : 9904181899 : Hi Friends.

One important thing to understand is the difference between an instance of an object and the object itself.

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Jatin Soni : 9904181899 : Hi Friends.

The Fundamental Built-in ASP Objects An ActiveX Object An ActiveX object (component) is similar to an Active Server Page built-in object. However, there is an important difference between the two. An instance of the object must be explicitly instantiated before it can be used.

I. Active Server Pages Objects – At a Glance Active

server

Pages

include

several

built-in

objects

and

installable ActiveX Components. These objects and components can be used to extend the power of your Active Server Page scripts. ASP derives their rich functionality from the user of six inherent objects that do have to be instantiated. These objects are special because they are built into Active Server Pages. These objects have their own predefined functionality and their own respective properties, methods, and events. The built-in Active Server Page objects provide control over the session and WebServer applications. These objects form the foundation of ASP development.  Application Object  Server Object  ObjectContext Object  Session Object  Request Object  Response Object Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends.

 Error (Err) Object

The Application Object The Application object is used to manage all information in the ASP application. The Application object is used to share information among several clients visiting the same group of pages. In ASP, the term application refers to all the .asp pages in a directory and its subdirectories. Only one instance of the Application object is created per application. It is shared among all the clients accessing that application. The information can be accessed and passed between different users in the application. Because multiple people can try to simultaneously change application variables, the Application object enables locking and unlocking of its variables. When a variable is locked other users cannot modify the properties of an Application object.

The Server Object The

Server

object

is

responsible

for

the

administrative

functionality of the server. The Server object provides a few basic properties and methods. The most important of these is the CreateObject method. One of the most exciting aspects of the Server object is the capability to create an instance of a server component via its CreateObject method. This capability to tap into existing ActiveX servers transforms the Web server from a simple file manager into a data translator. The MapPath method of the Server object maps a physical or virtual path to a directory on Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends.

the server. The ScriptTimeOut property determines the amount of time a script can run before the script process is terminated. The HTMLEncode methods enables HTML encoding of a string.  Tip:- Components are packages of related objects that you

can use in your pages. They make common ASP tasks easier, and add a great deal of power to your pages.

The ObjectContext Object The ObjectContext object is used by ASP to control transaction processing using the Microsoft Transaction Server (MTS). This direct processing within the MTS environment enables ASP to explicitly control, commit, and rollback features of objects managed by MTS.

The Session Object The Session object is responsible for managing information for a specific user session. The Session object refers to a single client accessing an application. Therefore, a new instance of the Session object is created of each session. The Session object is important to carrying information as a client travels between pages because Session variables persist for the entire session. One page can store data into a Session variable, and that data can be accessed from other pages in the session. These variables are not accessible by other user sessions, but they can be passed from page to page within the ASP application. The SessionID property uniquely identifies the particular user session. The Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends.

Timeout property sets the time in minutes that the SessionID is valid. Once the SessionID is invalid, the application destroys the user’s variables and the user must enter the application from the beginning. If the Timeout property is not reached, executing the Abandon method will destroy the specific user session.

The Request Object The

Request

object

is

primarily

responsible

for

retrieving

information/data from the client browser, and it uses five collections to provide for communication between the client browser and Web server.  Tip:- A collection is commonly referred to as a grouping of

common objects. When the client’s Web browser makes a request for a particular page, it sends some of information along to the server. That data is packaged together in the Request object. The Request object allows the page to retrieve what it needs – cookie information, information from a form, query string data, and more.  Tip:- Query

attached

at

string data is the extra stuff sometimes the

end

of

a

URL.

It

might

look

like

“?firstname=John&lastname=Smith”. The ClientCertificate collection retrieves certification fields from Web browsers. The Cookies collection enables the server to collect information from client-side cookies. The Form collection Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends.

retrieves values posted by a client form. Finally, the QueryString collection enables values to be parsed from the HTTP URL string. The Request object can also retrieve server environmental variables.

The Response Object The Response object is used to send output. The Response object is responsible for sending output from the server to the requesting client. The three most common Response object methods are the Write, Redirect, and Response methods. The Response object uses the Write method to send HTTP output to the user’s Web browser. The Response object can also control how and when data is sent and write cookies to store information. The Redirect method provides the capability to redirect the client browser to a different URL. The Response object enables a Cookie collection to set cookie values on the client’s browser.

Trapping errors with the Err object Active Server Pages use the error handling found in VBScript to process and manage runtime errors. VBScript handles error trapping with the Err object. The Err object has several properties and two methods. The Err object’s properties and methods can be accessed using the following syntax:

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Jatin Soni : 9904181899 : Hi Friends.

Err[.{property | method}] Where Err is the generated error object. The Err object’s properties provide information about the error object. These properties are listed below: The Err object’s Properties Property

Description

Description

Sets or returns the referenced error description.

Number

Sets or returns the number value of the error.

Source

Sets or returns the Application object that

generated the error. HelpFile

Sets or returns the fully qualified path to the help

file. HelpContext

Sets or returns the topic ID with the help file.

The Err object also provides methods that control it. The Err object’s methods, as shown below, can be used to generate a runtime error or rest the Err object’s properties. The Err object’s Methods Method

Description

Raise

Generates a runtime error.

Clear

Resets all object properties.

In VBScript code, the On Error statement is used to enable error handling. The Resume Next statement is used to respond to an error condition by enabling the program to continue execution with the next statement after the one that produced the error. Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends.

Therefore, to enable error handling in VBScript, use the following line of code: <% On Error Resume Next %> If no error handling is activated, any runtime error that is generated at the server will result in the immediate termination of the script. However, if error handling is activated, the application continues by executing the next line in the code.

Active Server Pages Objects – In Detail The Application Object The Application object is used to store and retrieve information that can be shared among all users of an application. For example,

One

can

use

the

Application

object

to

pass

information between users of the Web Site. Because more than one user can share the Application object, there are Lock and Unlock methods to ensure that multiple users do not try to alter an application object’s property/properties simultaneously. Syntax :- Application.method Methods :-

Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends. 

Lock :- The Lock method prevents other clients from modifying Application object properties simultaneously. The Lock methods blocks other clients from modifying the content of the variables stored in the Application object, ensuring that only one client at a time can alter or access the Application variables. Syntax :- Application.Lock



Unlock :- The Unlock method allows other clients to modify Application object properties. The Unlock method enables other

clients

to

modify

the

variables

stored

in

the

Application object after in has been locked using the Lock method. If this method is not called explicitly, the Web server unlocks the Application object when the script ends or times out. Syntax :- Application.Unlock

The Server Object The Server object enables to use the various utility functions on the server. For example one can use the server object to create instances of other objects. Syntax :- Server.method The Properties of Server object :

ScriptTimeout :- The ScriptTimeout property specifies the maximum amount of time a script can run before it is terminated. The timeout will not take effect while a server component is processing.

Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends.

Syntax :- Server.ScriptTimeout=NumSeconds The Methods of Server object :

CreateObject :- The CreateObject method creates an instance of a server component. If the component has implemented the OnStartPage and OnEndPage methods, the OnStartPage method is called at this time. Syntax :- Server.CreateObject(progID)



HTMLEncode :- The HTMLEncode method applies HTML encoding to a specified string. Syntax :- Server.HTMLEncode(string)



MapPath :- The MapPath method maps the specified relative or virtual path to the corresponding physical directory on the server. Syntax :- Server.MapPath(path)



URLEncode :- The URLEncode method applies URL encoding rules, including escape characters, to a specified string. Syntax :- Server.URLEncode(string)

Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends.

The Session Object The Session object can be used to store and retrieve information about particular sessions. One can use the Session object to store information that persists over the course of a visit by a user to your Web site. The Web server automatically creates Session object when a Web page from the application is requested by a user who does not already have a session. The server destroys the session object when the session expires or is abandoned. One common use for the Session object is to store user preferences set on a previous visit to the Web application. Session state is only maintained for browsers that support cookies. Syntax :- Session.property | method Properties :

SessionID – The SessionID property returns the session identification for this user. Each session has a unique identifier that is generated by the server when the session is created. The SessionID is returned as data type LONG. Syntax :- Session.SessionID



Timeout – The Timeout property specifies the timeout period for the Session object for this application, in minutes. If the user does not refresh a page within the Timeout period, the session ends. Syntax :- Session.Timeout[ = minutes]

Methods :Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends. 

Abandon – The Abandon method destroys all the objects stored in a Session object and releases their resources. If the Abandon method is not called explicitly, the server destroys these objects when the session times out. Syntax :- Session.Abandon

Events :- Scripts for the following events are declared in the GLOBAL.ASA file. They are Session_OnEnd and Session_OnStart.

The Request Object The Request object can be used to access all information sent in request from a browser to the server. The Request object can be used to retrieve information that a user has entered into an HTML form. The Request object retrieves the values that the client browser passed to the server during an HTTP request. Syntax :- Request.[Collection](variable) Collection of the Request Object :

ClientCertificate :- The values of fields stored in the client certificate

that

is

sent

in

the

HTTP

request.

The

ClientCertificate collection retrieves the certification fields (specified in the X.509 standard) from the request issued by the Web browser. If a Web browser uses the SSL3.0/PCT1 protocol (in other words, it uses a URL starting with “https://” instead of “http://”) to connect to a server and the server requests certification, the browser sends the certification fields. If no certificate is sent, the

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Jatin Soni : 9904181899 : Hi Friends.

ClientCertificate collection returns EMPTY. The web server must be configured to accept client certificates. 

Cookies :- The values of Cookies sent in the HTTP request. A Cookie is an ASP object that allows a programmer to store pertinent ”User data” either on the Web Server or on the Client’s computer in C:\Windows\Cookies for retrieval and use later. This data is largely used to maintain the ‘State’ of the connection between the Client and the Web server in ASP applications. Cookies can store other data as well. The Cookies collection enables you to retrieve the values of the cookies sent in an HTTP request. Syntax :- Request.Cookies(cookie)[(key)|attribute]



Form :- The values of Form elements in the HTTP request body. The form collection retrieves the values of form elements posted to the HTTP request body by a form using the POST method. Syntax :- Request.Form(parameter)[(index)|.Count]



QueryString :- The values of variables in the HTTP query string. The QueryString collection retrieves the values of the variables in the HTTP query string, that is, it retrieves the values encoded after the questing mark (?) in an HTTP request. It helps to extract and decode information through the use of GET method. Syntax:-

Request.QueryString(variable)[(index)|.

Count] Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends. 

Server

Variables

:-

The

values

of

predetermined

environment variables. The ServerVariables collection retrieves the values of environment variables. Syntax :- Request.ServerVariables(variable)

The Response Object One can use the Response object to send output to the client. The Response object is used to send information back to a browser. One can use the Response object to send output form the scripts to a browser. Syntax :- Response.collection|property|method 

Collections :- Specifies the type of collection. For example, Cookies – The Cookies collection sets the value of a cookie. If the specified cookie does not exist, it is created. If it exists, it takes the new value and the old value is discarded. Syntax:-Response.Cookies(cookie)[(key)|. attribute]=value

Properties Of The Response Object :

Buffer :- Indicates whether page output is buffered. The Buffer property indicates whether to buffer page output. When page output is buffered, the server does not send a response to the client until all of the server scripts on the current page have been processed, or until the Flush or End method has been called. The Buffer property cannot be set after the server has sent output to the client. For this reason,

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Jatin Soni : 9904181899 : Hi Friends.

the call to Response.Buffer should be the first line of the .asp file. Syntax :- Response.Buffer[=flag] 

Content Type :- Specifies the HTTP content type for the response. The Content Type property specifies the HTTP content type for the response. If no Content

Type is

specified, the default is “text/HTML” Syntax :- Response.ContentType[=Content Type] 

Expires :- Specifies the length of time before a page cached on a browser expires. The Expires property specifies the length of time before a page cached on a browser expires. If the user returns to the same page before it expires, the cached version is displayed. Syntax :- Response.Expires[=number]



Expires Absolute :- Specifies the date and time on which a page cached on a browser expires. The Expires Absolute property specifies the date and time at which a page cached on a browser expires. If the user returns to the same page before that date and time, the cached version is displayed. If a time is not specified, the page expires at midnight of that day. If a date is not specified, the page expires at the given time on the day that the script is run. Syntax :- Response.ExpiresAbsolute[=[date][time]]



Status :- The value of the status line returned by the server. The status property specifies the value of the status line

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Jatin Soni : 9904181899 : Hi Friends.

returned by the server. Status values are defined in the HTTP specification. Syntax :- Response.Status=StatusDescription Methods Of The Response Object:

AddHeader :- Sets the HTML header name to value. The AddHeader method adds an HTML header with a specified value. This method always adds a new HTTP header to response. It will not replace an existing header of the same name. Once a header has been added, it cannot be removed. This method is for advanced use only. Syntax :- Response.AddHeader(name, value)



AppendToLog :- The AppendToLog method adds a string to the end of the Web server log entry for this request. You can call it multiple times in one section of script. Each time the method is called it appends the specified string to existing entry. Syntax :- Response.AppendToLog string



Binary Write :- Writes the given information to the current HTTP output without any character-set conversion. The BinaryWrite method writes specified information to the current HTTP output without any character conversion. This method is useful for writing nonstring information such as binary data required by a custom application. Syntax :- Response.BinaryWrite data



Clear :- Erases any buffered HTML output. The Clear method erases any buffered HTML output. However, the

Jatin Soni : 9904181899 : Hi Friends.

Jatin Soni : 9904181899 : Hi Friends.

Clear method only erases the response body, it does not erase response headers. One can use this method to handle error cases. Syntax :- Response.Clear 

End :- Stops processing the .asp file and returns the current result. The End method causes the Web server to stop processing the script and returns the current result. The remaining contents of the file are not processed. Syntax :- Response.End



Flush :- Sends buffered output immediately. The Flush method sends buffered output immediately. Syntax :- Response.Flush



Redirect :- Sends a redirect message to the browser, causing it to attempt to connect to a different URL. The Redirect method causes the browser to attempt to connect to a different URL. Syntax :- Response.Redirect URL



Write :- Writes a variable to the current page. The Write method writes a specified string to the current HTTP output. Syntax :- Response.Write variant

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