Enterprise java unit-2_chapter-3

Enterprise Java
Unit-2
Chapter-3
• Session
By
Prof. Sandeep Vishwakarma

Session in Servlets
HTTP is a stateless protocol. All requests and responses are
independent. But sometimes you need to keep track of
client's activity across multiple requests. For eg. When a
User logs into your website, not matter on which web page
he visits after logging in, his credentials will be with the
server, until he logs out. So this is managed by a session.
The basic concept behind session is, 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.

How Session Works
Session is used to store everything that we can get from the client
from all the requests the client makes

Lifecycle of HttpSession?
HttpSession object is used to store entire session with a
specific client. We can store, retrieve and remove attribute
from HttpSession object. Any servlet can have access to
HttpSession object throughout the getSession() method of
the HttpServletRequest object.
• On client's first request, the Web Container generates a
unique session ID and gives it back to the client with
response. This is a temporary session created by web
container.
• The client sends back the session ID with each request.
Making it easier for the web container to identify where
the request is coming from.
• The Web Container uses this ID,finds the matching session
with the ID and associates the session with request .

Servlet: HttpSession Interface

Session Management
Session Management is a mechanism used by
the Web container to store session information
for a particular user. There are four different
techniques used by Servlet application for session
management.
They are as follows-
• Cookies
• Hidden form field
• URL Rewriting
• HttpSession

1.Cookies
Cookies are small pieces of information that are sent
in response from the web server to the
client. Cookies are the simplest technique used for
storing client state.
Cookies are stored on client's computer. They have a
lifespan and are destroyed by the client browser at
the end of that lifespan.
Using Cookies for storing client state has one
shortcoming though, if the client has turned of
Cookie saving settings in his browser then, client
state can never be saved because the browser will
not allow the application to store cookies.

Advantages and Disadvantages of Cookies
Advantages
• Simplest technique of maintaining the state.
• Cookies are maintained at client side.
• Cookie information can be extracted from the
client request using getCookies() of
HttpSevletRequest
Disadvantages
• It will not work if cookie is disabled from
the browser.
• Only textual information can be set in
Cookie object.

2.URL Rewriting for Session Management
If the client has disabled cookies in the browser then session
management using cookie wont work. In that case URL
Rewriting can be used as aback up. URL rewriting will always
work.
In URL rewriting, a token(parameter) is added at the end of
the URL. The token consist of name/value pair separated by
an equal(=) sign.
For Example:

Advantages:
• It will always work whether cookie is disabled
or not (browser independent).
• Extra form submission is not required on each
pages.
Disadvantages:
• It will work only with links.
• It can send Only textual information.
Advantages and Disadvantages of URL Rewriting

3.Hidden Form Field for Session Management
Hidden form field can also be used to store session
information for a particular client. In case of hidden
form field a hidden field is used to store client
state. In this case user information is stored in
hidden field value and retrieved from another
servlet.
This approach is better if we have to submit form in
all the pages and we don't want to depend on the
browser

Advantages:
• It will always work whether cookie is disabled or
not.
• Inserting a simple HTML Input field of type hidden
is required. Hence, its easier to implement.
Disadvantages:
• It is maintained at server side.
• Extra form submission is required on each pages.
• Only textual information can be used.
Advantages and Disadvantages of Hidden Form Field

4. HTTP Session Management
In this case, container creates a session id for each user.
The container uses this id to identify the particular user.An
object of HttpSession can be used to perform two tasks:
• bind objects
• view and manipulate information about a session, such
as the session identifier, creation time, and last
accessed time.

Advantages:
• It stores user states and data to all over the application.
• Stores every user data separately.
• Session is secure and transparent from user because
session object is stored on the server
Disadvantages:
• Performance overhead in case of large number of user,
because of session data stored in server memory.
Advantages and Disadvantages of HTTP Session

Example for demonstrating usage of
HttpSession
Following pages are used for Demonstrating
HTTP Session
• Index.html
• Validate.java
• Welcome.java
• web.xml

Index.html
<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>

Validate.java
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"))
{
HttpSession session = request.getSession(); //creating a session
session.setAttribute("user", name);
response.sendRedirect("Welcome");
} } }

Welcome.java
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
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);
} }

web.xml
<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>

Enterprise java unit-2_chapter-3

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