Session Management

© FPT SOFTWARE – TRAINING MATERIAL – Internal use 04e-BM/NS/HDCV/FSOFT v2/3

Session Management


Review

Page-centric designs in JSP are called Model 1 architecture Model 1 architecture is used for simple applications and generates

dynamic content Model 2 architecture is suitable for large and complex applications as

it uses a combination of servlets and JSP Model 2 applications are based on Model-View-Controller (MVC)

pattern MVC pattern contains a Model, View, and Controller RequestDispatcher interface forwards the request from a JSP page or a

servlet to other resources, such as HTML file, servlet, or a JSP page The two methods in RequesDispatcher interface are include() and

forward() Errors in JSP page include Translation time and Request time errors


Objectives

Define session Explain and implement session tracking

mechanism Describe session lifecycle Extend Java Server Pages


Introducing Session

A long-term connection using the session layer of a network protocol

The Web server identifies requests and responses across a network connection as a single working session

Session acts as a link between the Web server and the client events

Web server uses the session to post client events to the server objects


Introducing Session - Contd…

JSP uses the sessions to store unique data of a particular client connected to a Web application

Sessions for two Web browsers (Clients)


Methods in Session

Methods Description

getAttribute() Returns the object with specified name defined in the session. The getAttribute() method returns null if object is not found

getAttributeNames() Returns list of objects defined in the session

getCreationTime() Returns the creation time of the session in milliseconds since midnight January 1, 1970 GMT

getId() Returns the unique identifier which is the session Id, as a string

getLastAccessedTime() Returns the time of last client request with the session. The time is returned as number of milliseconds since midnight January 1, 1970 GMT


Methods in Session - Contd…

Methods Description

getMaxInactiveInterval()

Returns the maximum time interval of the session. The servlet container keeps the session open till the user accesses the Web site

removeAttribute()

Removes the object associated with the specified string from the session

setAttribute() Associates an object with the specified key string and stores it to the session

setMaxInactiveInterval()

Specifies the time interval in seconds between the client requests before the servlet container will invalidate this session


Overview of Session Tracking Mechanisms

Maintains a session till the user is browsing the Web site Used in interactive Web applications to store the information

of the user logged in to the Web site The information stored is used to identify the user sending a

request to the Web server Session tracking helps to maintain the session information and

keeps track of the multiple requests made by the client


Implementing Session Tracking – Mechanisms

Server-side technologies maintain the information on the Web server

The server creates a session Id for the user logged in to the Web site and sends the session Id to the user computer

The session tracking feature contained in the servlets or JSP container maintains the state of a Web browser


Session Tracking - Contd…

Information is sent to the browser in three ways, which include: Cookies URL Rewriting Hidden form field method

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Mention the scenarios where each is used


Cookies

Cookies are text files stored on the user’s computer containing the session Id of the user sent by the Web server

The cookie is sent back to the Web server with every subsequent request made by the user in the same session

The cookie includes a name, a single value and optional attributes

Cookies are used for maintaining sessions and do not have an expiration time


Cookies – Contd…

Cookies help to maintain a single session for a user browsing the Web site


Cookies – Contd…

Advantages of Cookies are: Remember user IDs and password. To track visitors on a Web site for better service and

new features. Cookies enable efficient ad processing.

Disadvantages of Cookies are:The size and number of cookies stored are limited.Personal information is exposed to the other users.Cookies fails to work if the security level is set too high

in the Internet browser.


URL Rewriting

JSP hides the details of a cookie-based session tracking and supports the URL rewriting mechanism

URL Rewriting works with Web browsers that do not support cookies or the cookies that are disabled on a Web browser

Each URL that references the Web browser is returned to the user and contains additional information


URL Rewriting – Contd…

The session ID is encoded in the URLs that are created by the JSP pages



<b>Search results for books</b><form method="post" action="serverprogram.jsp"><input type="checkbox" name="productID" value="100">CD MP3 Converter Kit For Your CAR<br><input type="checkbox" name="productID" value="101">Front Loading Car MP3/CD Player With Anti Shock Memory and FM<br><input type="checkbox" name="productID" value="102">CAR/Home DVD/VCD/MP3 Playerwith anti shock for Indian Roads<br><input type="submit" name="Submit" value="Add to Cart"><br></form>

URL of server side program

Provides check box for different products

Submits the user input to URL


URL Rewriting - Contd…

<b>Search results for books</b><form method="post" action="serverprogram.jsp?productID=102"><input type="checkbox" name="productID" value="150">DVD Player with built in Amplifier <br><input type="checkbox" name="productID" value="160">Ultra Slim DVD Player Multi Region 5.1 Digital<br><input type="submit" name="Submit" value = "Add to Cart"><br></form>

URL for server side program after the user selects a product and goes to another page

Provides check box for different products

Submits input to the URL

http://shopping.indiatimes.com/webapp/commerce/command/ExecMacro/Indiatimes_Shop/macros/singlemacrosnew/Product.d2w/report?prmenbr=195102&prrfnbr=876324&parentcat=753736&product_rn=876324&merchant_rn=195102&catrfnum=753738&cgrfnbr=753738&title=DVD%20player%20with%20Built%20in%20Amplifier%20%3Cfont%20color=red%3E%20%3Cb%3EFree%20CD%20lens%20Cleaner%20worth%20Rs.150%20/-%3C/b%3E%3C/font%3E&testURL=%2Fwebapp%2Fcommerce%2Fcommand%2FCategoryDisplay%3Fparentcat%3D753736%26cgmenbr%3D195102%26cgrfnbr%3D753738%26merchant_rn%3D195102%26title%3DDVD%20Players%26what%3DDVD%20Players



Disadvantages of Cookies are: Server side processing is tedious. Every URL that is returned to the user should

have additional information appended to it. If the user leaves the session and opens the

Web page using a link or bookmark then the session information is lost .


Hidden Form Fields Method

Information from the Web browser is returned to the Web server in the form of HTTP parameters

Utilizes the hidden fields in an HTML page Hidden fields in the form are used to send the

information to the Web browser Stores information about a session Helps to carry the information from one HTML page

to another


Hidden Form Fields – Contd…

When the user visits the next page, the server side program reads all the parameters that a user passes in the previous form


Hidden Form Fields Example

<b>Search results for books</b>

<form method="post" action="serverprogram.jsp">

<input type="hidden" name="productID" value="100">

<input type="checkbox" name="productID" value="150">DVD Player with Built in Amplifier <br><input type="checkbox" name="productID" value="160">Ultra Slim DVD Player Multi Region 5.1 Digital<br>

<input type="submit" name="Submit" value="Add to Cart"><br></form>

Hidden input field

Provides check box for user input

Submits user input to the server side program

http://shopping.indiatimes.com/webapp/commerce/command/ExecMacro/Indiatimes_Shop/macros/singlemacrosnew/Product.d2w/report?prmenbr=195102&prrfnbr=876324&parentcat=753736&product_rn=876324&merchant_rn=195102&catrfnum=753738&cgrfnbr=753738&title=DVD%20player%20with%20Built%20in%20Amplifier%20%3Cfont%20color=red%3E%20%3Cb%3EFree%20CD%20lens%20Cleaner%20worth%20Rs.150%20/-%3C/b%3E%3C/font%3E&testURL=%2Fwebapp%2Fcommerce%2Fcommand%2FCategoryDisplay%3Fparentcat%3D753736%26cgmenbr%3D195102%26cgrfnbr%3D753738%26merchant_rn%3D195102%26title%3DDVD%20Players%26what%3DDVD%20Players


Hidden Form Fields – Contd…

The advantages of hidden form fields are: Simplest way to implement session tracking Displays nothing on the HTML page but can be used to

hold any kind of data Helps to maintain a connection between two pages

The disadvantage of hidden form fields is that this method of session tracking displays sensitive information to the user.

The information includes the data passed around to maintain a session.


Session Life Cycle

The server assigns a unique ID to the session created for a particular user request.

This session ID is passed to the client as a cookie or a hidden variable.

The session is considered new until the client returns the session ID to the server through a cookie or as a part of the requested URL.

A session exists on the server until it becomes invalid or the server is stopped.

The HttpSession objects are used to store the session data in the current servlet context.


Using Session Object

Session object can be used to store and read data.

The session object acts almost like a bulletin board from where the objects can be written or read


Using Session Object - Contd…

……// Obtain a session objectHttpSession session = request.getSession(true); //Add an item to the session Integer sessionData = new Integer (100);Session.putValue(“IntValue”, sessionData);……

Obtains a session object

Adds item to the session object

The request() method requests for the session object.


Using Session Object - Contd…

…// Obtain a session objectHttpSession session = request.getSession(true);// Read the session data and cast it to the appropriate object typeInteger sessionInt = (Integer) session.getValue(“session”);int count = sessionInt.intValue();……

Obtains a session object

Reads the session valueCasts the session

value to appropriate datatype

The session value can be read and cast to the appropriate object type.


Using Session Objects – Contd…

<% String sessionval=(String)session.getAttribute("userid")); if(sessionval == null) { session.setAttribute("userid",sessionval); out.println(session.getAttribute("userid")); } else { out.println("User Session already created"); }%><b>click this link to<a href="<%=session.removeAttribute("userid")%>">remove session attribute</a></b><br/><b>click this link to <a href="<%=session.invalidate()%>"> invalidate the session</a></b><br/>

Accepts userid

If sessionval is null, the value of sessionval is set to userid.

Removes the session

Invalidates the session

The session can be invalidated using the invalidate() method of the HttpSession object.


Using Session Object – Contd…

The binding of objects to a request object is similar to the storing of the object in a session

An object bound to a request is available only for the life of that particular request

An object can be bound using the setAttribute(String key, Object obj) method in the HttpRequest interface

An object can be retrieved using the getAttribute(String key) method.


Extending Java Server Pages

The superclass may offer several benefits, such as, a set of utilities, which may not be offered by the standard packages

In order to extend a JSP from a superclass, both the superclass and the extended JSP must follow several requirements


Superclass

A superclass must implement the HttpJspPage interface to use the HTTP protocol or it must implement the JSP interface.

The superclass should include: All methods from the Servlet Interface and must be

declared as final. The Service() method that should invoke the

_jspService() method. The init() method that should invoke the jspInit()

method. The destroy() method that should invoke the jspDestroy() method


JSP Sub-class

A JSP sub-class should provide jspInit() method and jspDestroy() method.

<%@ page extends = “servlet.JSPBase” %><%! public void jspInit(){ } public void jspDestroy(){ }%><% out.println(“<B> User Name: </B>” +

getUser(request) + “<P>”); out.println(“<B> Catalog: </B>” + getCatalog(request));%>

Empty methods that satisfy the JSP sub-classing conditions


Summary Session is a long-term connection that uses the session layer of a network layer

protocol Session acts as a link between the server and the client events Web server uses the session to post client events to the server objects Server objects utilize the session for passing messages to the client and listening to

client events The different methods of session object includes:

getAttribute() getAttributeNames() getCreationTime() getId() getLastAccessedtime() getMaxInactiveInterval() removeAttribute() setAttribute() setMaxInactiveInterval()


Summary – Contd…

Session tracking maintains a session till the user browses the Web site The session tracking feature contained in the servlets or JSP container

maintains the state of a Web browser Cookies are text files stored on the user’s computer containing the session Id

of the user, sent by the Web server A Cookie is sent back to the Web server with every subsequent request made

by the user in the same session URL rewriting works with Web browsers that do not support cookies or the

cookies that are disabled on a Web browser The information from the Web browser is returned to the server in the form

of HTTP parameters Hidden form fields are used to store information about a session. Hidden form field helps to carry the information from one HTML page to

another HTML page


Summary – Contd…

The server assigns a unique ID to the session created for a particular user request.

The HttpSession object is defined by the HttpSession interface, and is obtained using the getSession() method of the HttpServletRequest object.

Session object can be used to store and read data and acts almost like a bulletin board from where the objects can be written or read.

When the reading or writing operation is complete, the session can be invalidated using the invalidate() method of the HttpSession object.

Binding of objects to a request object is similar to the storing of the object in a session.

An object can be bound using the setAttribute(String key, Object obj) method in the HttpRequest interface, and can be retrieved using the getAttribute(String key) method.

A superclass must implement the HttpJspPage interface to use the HTTP protocol or it must implement the JSP interface.

A JSP sub-class should provide jspInit() method and jspDestroy() method.


Q & A

Session Management

Documents

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