Object Model

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ACTIVE SERVER PAGES OBJECT MODEL The ASPs server component, ASP.DLL contains built-in objects that are readily available to the user when an ASP application is created. There are seven main objects that comprise the ASPs object model as in the list below: • Request Object • Response Object • Session Object • Application Object • Server Object • Object Context Object • ASP Error Object

REQUEST OBJECT 1

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9 Request object handles all of the requests from the user, including data from cookies, forms and security certificates. This object is used when getting information from the user. An overview of Request Object Collections Client Certificate

Events

Methods

Properties

Binary Read

Total Bytes

Cookies Form Query String Server Variable

Reading binary data from the user This method is used to read the specified number of bytes directly from the http request body sent by the client using post method into an asp program. Syntax: Special array name=request.binaryread(no of bytes)

Cookies: cookies are small files of clear text that contain information such as user preferences when changing pages within a site or for subsequent visits. Servervariables Syntax: Variable=request.servervariables (name of the environment variable)

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9 Some of the commonly used environment variables are given below: 1.URL

The complete path except the query string.

2.PATH_INFO

The complete path except the query string.

3.PATH_TRANSLATED

The full physical path of the currently executed ASP program.

4.APP_PHYSICALPATH

The physical directory.

5.QUERY_STRING

Just the query string portion of the URL.

6.SERVER_NAME

The name of the computer that is running the web server.

7.SERVER_SOFTWARE

The type of the web server along with its version number.

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address

of

the

server’s

root

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RESPONSE OBJECT Response Object handles the task of sending data back to the user. Response Object’s write method can be used explicitly and implicitly. Response Object’s Is Client Connected property checks to see if connection between the user or client is still alive, which relies on session object behind the scenes.

The The the the

An overview of Response Object Collections Cookies

Events

Methods

Properties

Add Header

Buffer

Append To Log

Cache Control

Binary Write

Char Set

Clear

Content Type

End

Expires

Flush

Expires Absolute

Redirect

Working with buffer The output to a client can be sent by the server in 2 different ways namely 1. Buffered

output: The buffered PICs output is not sent Status until the script is finished i.e., the complete output of the script is sent at once. 2. Un –Buffered output: An un-buffered output is sent immediately as each line is created. Write

IsClientConnect ed

In order to send buffered output to the client we can use the property buffer of response object 2

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9 Syntax: Response.buffer=booleanvalue[it can be true or false]

Common status values Status Value

Short Description

200

Ok

201

Created

202

Accepted

204

No Content

301

Moved Permanently

302

Moved Temporarily

304

Not Modified

400

Bad Request

401

Unauthorized

403

Forbidden

404

NA Found

500

Internet Server Error

501 1. response.write

Not Implemented

502 Bad Gateway 2. response.binarywritebinaryarray 3. response.redirect=URL 503 Service Unavailable 4. response.addheader(“header name”,”header value”)

Syntax for methods of response object: 5. response.appendtolog(string) 6. <%response.clear%> 1 7. <%response.end%>

8. <%response.flush%>

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Setting Page Expiration

The user can set for the user’s browser to cache the page. If it is to be cached, how long? The web pages should be cached on the client’s machine, the response object is provided with two properties. They are: – Expires – Expires Absolute Expires Using this property we can specify for how long? The client’s machine should cache the current page in terms of minutes. Syntax: <%response.expires=time in minutes%>

Expires Absolute If we want a particular page to be removed from the client’s machine on a particular date and time, we can use the Expires Absolute property of the Response Object. Syntax: <%response.expiresabsolute=#date, 2 time#%>

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Checking if the user is still connected Sometimes, we may face a situation that to check whether or not the user is still connected in such scenarios we can use the property of Response Object called “IsClientConnected” Syntax: < %response.isclientconnecte

Setting the content type In order to inform the browser about the type of content that is present in a response from the server, we can use property called “Content type”. Syntax: Response.contenttype=”maintype/s ubtype”

Clear When clear method is invoked the response body of the http is erased Syntax: < %response.clear

End The End method causes the server to stop the execution the script and send any buffered output. Syntax: <%response.end %>

Flush 2

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9 This method immediately sends any previously buffered output to the client but continues the processing of the script. Syntax: <%response.flush%>

SESSION OBJECT Session Object maintains a connection between an ASP application and each user. The session object prevents users from having to authenticate repeatedly. Session object helps to maintain variables or information required for the entire session. Session object relies on cookies. An overview of session object Collections

Events

Methods

Properties

Contents

Onstart

Abandon

Codepage

Staticobjects

Onend

Contents.remove

LCID

Contents.remove all

SessionID TimeOut

Properties Session: The interval an user spends after he has made a request to one of the pages and before the user abandons it either through the code or after the specified timeout value has reached is called a session. Session Id: Each user is given an unique number usually known as sessionid at the beginning of his session that is stored on the web server. 1

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9 The sessionid is then written automatically into a cookie on the client’s machine. The sessionid value can be determined from within an ASP script as follows <% dim idval Idval=session.sessio nID %>

Timeout: A timeout can also be set for the user sessions. The time period for which the server will maintain a session for a user can be important. Default timeout is 20 minutes. Note: the default timeout depends on the version of IIS. Syntax: <%session.timeout=time in minutes %>

Codepage: A page that contains the character set used by a specific locale with all the alphanumeric characters and punctuations is called a code page. The different code pages are identified by a unique number called codepage id. Syntax: Session.codepage =ID

LCID: The acronym for LCID is Location Identifier. The user can set his ASPs to use a specific system locale by setting the location identifier. This helps to set the locale for an ASP to present information in a more suitable manner. 3

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9 Syntax: Session.LCID=val ue

Events Onstart: This event is triggered when a user who has not instantiated a session on the web server requests any page from the server i.e., begins a session. The code for this event if exists resides in the global.asa file. This code is executed well before executing any code of the requested page.

Sub session_onstart ------------------End sub

Onend: This event is triggered either when the user’s session times out or when the ASP program invokes the abandon method of the session object. The code for this event if exists resides in global.asa file. Sub session_onend ---------1 ----------

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Methods Abandon: The session object’s abandon method can be used to clear all the session variables in one step. Syntax: Session.aband on

Contents.remove: removes a single item from the contents collection with contents.remove method. Syntax: Session.contents.remove(object name)

Contents.removeall: removes all items in the session. Syntax: Session.contents.remov eall

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APPLICATION OBJECT Application Object basically all of the files contained within a virtual directory and all of its subdirectories. So a collection of files that make up a particular ASPs site are referred to as ASPs applications or ASP applications. The user can also access all of the global variables and objects that are in global, as a file, through the use of Application Object. Collections

Events

Methods

Contents

OnEnd

Contents.remove

Staticobjects

OnStart

Contents.remove all

Lock

Properties

Unlock

Note: There are no properties for application object. Using Locking Mechanisms with the application object The application object offers lock method and the unlock method to keep track of the variables used by many ASPs. Both the events require no arguments. The user has to first use the Lock method and then the unlock event as follows: <% Application.lock Statements 1 Application.unlock

%>

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Fact: collections, events are same as session object. In the application object apart from onstart and onend events there are other two events namely lock and unlock.

SERVER OBJECT The server object is the web server. This object is used to incorporate some of the server’s own functionality into the ASPs. The object can be used to handle script time outs to execute other ASPs from within an ASP. An overview of server object Collections

Events

Methods

Properties

Createobject

scriptTimeOut

Execute Getlasterror HTMLencode Mappath Transfer URL Encode

PROPERTIES ScriptTimeOut: The server object’s ScriptTimeOut property is used to set a timeout for the ASPs. The default time out for every script in ASP is 90 seconds unless the timeout is altered explicitly. 1

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9 Syntax: Server.scripttimeout=an integer value

METHODS

CreateObject: method is used to create an instance of non-intrinsic objects. Syntax: Dim name of the instance variable Set name of the instance=server.createobject(“name of the object that should be used”)

Execute: method is similar to the response object’s redirect method. The redirect method will send information back to the client but the execute method will handle the calling entirely on the server. The user can split the script into smaller parts that can be accessed without performance loss. It will also return the calling script. Syntax: Server.execute(“name of ASP file”)

HTMLEncode: method allows us to display the source code of html page on the client’s browser without allowing it to interpret them. Syntax: Servre.HTMLEncode(“a set of html tags”)

MapPath: is used to determine the physical path of the file. This method takes virtual path or relative path as a parameter and converts it into a physical path. Syntax: String name=server.mappath(“virtual string”)

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9 Transfer: method is like the execute method, but does not return to the original script. Syntax: Server.transfer(“name of a different ASP file”)

Getlasterror: The ASP scripts raise 3 different types of errors namely 1. Pre-processing errors: are raised when the ASP pre-processor is

unable to find a file that is mentioned in the include directive.

2. Script compiling errors: are raised when the script compiler finds

an unrecognized token or missing the required keyword. 3. Run time errors: are raised due to a variety of factors such as logical errors or missing or locked or altered resources. Syntax: Set strvariable=server.getlasterr

URLEncode: method helps to encode a string so that it appears when passed to a URL. It is used instead of the GET method to send the data over the URL. Syntax: Strvariavle=server.URLEncode(“URL string”)

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OBJECT CONTEXT OBJECT Object context object handles transactions, where an entire sequence of steps either succeeds or fails as a whole. This object can be used with Microsoft Transaction Server MTS and COM+ component services. Collections

Events

Methods

Ontransactionabor t

Setabort

Properties

Setcomplete

Ontransactioncom mit

METHODS Set Abort: If a transaction has become a failure, the entire transaction should be aborted. Syntax: Objectcontext.seta bort

Set Complete: this method can be invoked to indicate the transaction is being successful. Syntax: Objectcontext.setcomp lete

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EVENTS Ontransactioncommit: helps to use a sub routine that informs the user of the success of a particular transaction that was requested. Syntax: <% Sub ontransactioncommit ------------------------------------End sub %> Ontransactionabort: is used when the user is able to use a subroutine that informs the user of the failure for the particular transaction that was requested.

Syntax: <% Sub ontransactionabort ----------------------------End sub %>

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ASP ERROR OBJECT ASP Error Object provides greater error handling information that the error object which comes with VBscript and is new addition in ASP3.0. The ASP error object to catch bugs and errors in the scripts and code.

Collections

Events

Methods

Properties ASPcode ASPdescription Category Column Description File Line Number Source

Category property lets to know whether it is a run time error or syntax error or a preprocessing error. Number property is standard COM error number-a long value. Line and Column property indicate the line and the column respectively of the first character that the server encountered where the error occurred. File property lets to know what file the error occurred in. Description property gives short description of what the error was and the ASP description property gives a lengthier description of the problem. 1

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9 ASPcode property is a code that IIS assign to specify ASP’S error. Source property displays the actual line of script where the error occurred. It is helpful with syntax error.

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