session tracking in servlets - sns courseware

Session Tracking in Servlets

• Session simply means a particular interval of time.

• Session Tracking is a way to maintain state (data) of an user. It

is also known as session management in servlet.

• Http protocol is a stateless so we need to maintain state using

session tracking techniques. Each time user requests to the

server, server treats the request as the new request. So we need

to maintain the state of an user to recognize to particular user.

• HTTP is stateless that means each request is considered as the

new request.

Session Tracking Techniques

There are four techniques used in Session tracking:

1. Cookies

2. Hidden Form Field

3. URL Rewriting

4. HttpSession1

16CS302/Internet Programming/Session

Handling – Understanding

Cookies/K.Maheswari AP/CSE

• whenever a user starts using our application, we can save a unique

identification information about him, in an object which is available

throughout the application, until its destroyed.

• So wherever the user goes, we will always have his information and

we can always manage which user is doing what. Whenever a user

wants to exit from your application, destroy the object with his

information.

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<form method="post" action="Validate">

User: <input type="text" name="user" /><br/>

Password: <input type="text" name="pass" ><br/>

<input type="submit" value="submit">

</form>

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Index.html

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class Validate extends HttpServlet {

protected void doPost(HttpServletRequest request, HttpServletResponse

response) throws ServletException, IOException

{

response.setContentType("text/html;charset=UTF-8");

String name = request.getParameter("user");

String pass = request.getParameter("pass");

if(pass.equals("1234"))

{

//creating a session

HttpSession session = request.getSession();

session.setAttribute("user", name);

response.sendRedirect("Welcome"); } }}

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Validate.java

import java.io.*;



public class Welcome extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse

response) throws ServletException, IOException

{

response.setContentType("text/html;charset=UTF-8");

PrintWriter out = response.getWriter();

HttpSession session = request.getSession();

String user = (String)session.getAttribute("user");

out.println("Hello "+user);

}

}

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<web-app..>

<servlet>

<servlet-name>Validate</servlet-name>

<servlet-class>Validate</servlet-class>

</servlet>

<servlet>

<servlet-name>Welcome</servlet-name>

<servlet-class>Welcome</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>Validate</servlet-name>

<url-pattern>/Validate</url-pattern>

</servlet-mapping>

<servlet-mapping>

<servlet-name>Welcome</servlet-name>

<url-pattern>/Welcome</url-pattern>

</servlet-mapping>

<welcome-file-list>

<welcome-file>index.html</welcome-file>

</welcome-file-list>

</web-app>

Web.xml

Cookies

• small piece of information that is persisted between the multiple client

requests name, a single value, and optional attributes such as a comment,

path and domain qualifiers, a maximum age, and a version number.

• A web server can assign a unique session ID as a cookie to each web

client and for subsequent requests from the client they can be recognized

using the received cookie.

• used for storing client state

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Types of Cookie

There are 2 types of cookies in servlets.

1. Non-persistent cookie

2. Persistent cookie

Non-persistent cookie

It is valid for single session only. It is removed each time when

user closes the browser.

Persistent cookie

It is valid for multiple session . It is not removed each time when

user closes the browser. It is removed only if user logout or

signout.

Advantage of Cookies

1. Simplest technique of maintaining the state.

2. Cookies are maintained at client side.

Disadvantage of Cookies

1. It will not work if cookie is disabled from the browser.

2. Only textual information can be set in Cookie object.9




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create Cookie

Cookie ck=new Cookie("user","sony");//creating cookie object

response.addCookie(ck);//adding cookie in the response

delete Cookie

Cookie ck=new Cookie("user","");//deleting value of cookie

ck.setMaxAge(0);//changing the maximum age to 0 seconds


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import java.io.*;



public class FirstServlet extends HttpServlet {

public void doPost(HttpServletRequest request, HttpServletResponse response){

try{

response.setContentType("text/html");


String n=request.getParameter("userName");

out.print("Welcome "+n);

Cookie ck=new Cookie("uname",n);//creating cookie object


//creating submit button

out.print("<form action='servlet2'>");

out.print("<input type='submit' value='go'>");

out.print("</form>");

out.close();

}catch(Exception e){System.out.println(e);}

} } 14




import java.io.*;



public class SecondServlet extends HttpServlet {

public void doPost(HttpServletRequest request, HttpServletResponse response){

try{

response.setContentType("text/html");


Cookie ck[]=request.getCookies();

out.print("Hello "+ck[0].getValue());

out.close();

}catch(Exception e){System.out.println(e);}

}

} 15




<web-app>

<servlet>

<servlet-name>s1</servlet-name>

<servlet-class>FirstServlet</servlet-class>

</servlet>

<servlet-mapping>


<url-pattern>/servlet1</url-pattern>

</servlet-mapping>

<servlet>


<servlet-class>SecondServlet</servlet-class>

</servlet>

<servlet-mapping>


<url-pattern>/servlet2</url-pattern>

</servlet-mapping>

</web-app>

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Hidden Form Fields:

• a hidden (invisible) textfield is used for maintaining the state of an user

• <input type="hidden" name="sessionid" value="12345">

• we store the information in the hidden field and get it from another

servlet

• when the form is submitted, the specified name and value are

automatically included in the GET or POST data. Each time when web

browser sends request back, then session_id value can be used to keep

the track of different web browsers.

URL Rewriting

append some extra data on the end of each URL that identifies the session,

and the server can associate that session identifier with data it has stored

about that session.

http://point.com/file.htm;sessionid=12345

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session tracking in servlets - sns courseware

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