JavaOmar Rana

University of South Asia

Revisiting Session Tracking

HTTP is a stateless protocol Every request is considered

independent of every other request

Many web applications need to maintain a conversational state with the client A shopping cart is a classic example

Store State Somewhere

Server Side?

Makes Server Really Complicated

State per client!

Client Side?

“Post-Notes”

Server puts little notes on the client side

When client submits the next form, it also (unknowingly) submits these little notes

Server reads the notes, remembers who the client is

Three Typical Solutions

Cookies

URL Rewriting

Hidden Fields

Handling Cookies

Potential of Cookies Idea

Web server sends a simple name-value pair to client (web browser etc.)

Saved by the client

Later, Client returns same name and value when it connects to same site (or same domain, depending on cookie settings)

Potential of Cookies

Typical Uses of Cookies

Identifying a user during an e-commerce session

Servlets have a higher-level API for this task

Avoiding username and password

Customizing a site

Focused advertising

Sending Cookies to Browser Create a Cookie object

Cookie c = new Cookie("name", "value");

Set the Maximum age etc Cookie persists on disk

c.setMaxAge(seconds);

// Set other attributes.

Place the Cookie into HTTP response If you forget this step, no cookie will be sent to the

browser

response.addCookie(c);

Reading Cookies from Browser To read incoming cookies, get them from request object

Cookie[] cookies = request.getCookies();

Once you have an array of cookies, you can iterate over it Use getName and getValue to retrieve cookie name & value

respectively

for(int i=0; i<cookies.length; i++) {

Cookie c = cookies[i];

if (c.getName().equals("someName")){ // doSomethingWith cookie break; } }

Example 1: RepeatVisitor This servlet checks for a unique cookie, named

“repeat”.

If the cookie is present, servlet says “Welcome Back”

Otherwise, servlet says “Welcome Aboard”.

Example CodeRepeat Visitor

Using Cookies to Detect First-Time Visitors (Results)

HTTP Cookies

String sID = makeUniqueString();

Hashtable sessionInfo = new Hashtable();

Hashtable globalTable = findTableStoringSessions();

globalTable.put(sID, sessionInfo);

Cookie sessionCookie = new Cookie("JSESSIONID", sID);

response.addCookie(sessionCookie);

1239865610

Credit: cs193i at Standford

HTTP Cookies

String sID = makeUniqueString();

Hashtable sessionInfo = new Hashtable();

Hashtable globalTable = findTableStoringSessions();

globalTable.put(sID, sessionInfo);

Cookie sessionCookie = new Cookie("JSESSIONID", sID);

response.addCookie(sessionCookie);

1239865610

Credit: cs193i at Standford

HTTP Cookies

String sID = makeUniqueString();

Hashtable sessionInfo = new Hashtable();

Hashtable globalTable = findTableStoringSessions();

globalTable.put(sID, sessionInfo);

Cookie sessionCookie = new Cookie("JSESSIONID", sID);

response.addCookie(sessionCookie);

1239865610

Credit: cs193i at Standford

HTTP Cookies

String sID = makeUniqueString();

Hashtable sessionInfo = new Hashtable();

Hashtable globalTable = findTableStoringSessions();

globalTable.put(sID, sessionInfo);

Cookie sessionCookie = new Cookie("JSESSIONID", sID);

response.addCookie(sessionCookie);

1239865610

Credit: cs193i at Standford

HTTP Cookies

String sID = makeUniqueString();

Hashtable sessionInfo = new Hashtable();

Hashtable globalTable = findTableStoringSessions();

globalTable.put(sID, sessionInfo);

Cookie sessionCookie = new Cookie("JSESSIONID", sID);

response.addCookie(sessionCookie);

1239865610

JSESSIONID → 1239865610

Credit: cs193i at Standford

HTTP Cookies

String sID = makeUniqueString();

Hashtable sessionInfo = new Hashtable();

Hashtable globalTable = findTableStoringSessions();

globalTable.put(sID, sessionInfo);

Cookie sessionCookie = new Cookie("JSESSIONID", sID);

response.addCookie(sessionCookie);

1239865610

Set-Cookie: JSESSIONID=1239865610;

Credit: cs193i at Standford

HTTP Cookies

// On request

String sID = getCookieValue("JSESSIONID");Hashtable globalTable = findTableStoringSessions();Hashtable sInfo = (Hashtable) globalTable.get(sID);

// sInfo contains the data related to user

Cookie: JSESSIONID=1239865610;

Credit: cs193i at Standford

HTTP Cookies

// On request

String sID = getCookieValue("JSESSIONID");Hashtable globalTable = findTableStoringSessions();Hashtable sInfo = (Hashtable) globalTable.get(sID);

// sInfo contains the data related to user

Cookie: JSESSIONID=1239865610;

Credit: cs193i at Standford

HTTP Cookies

// On request

String sID = getCookieValue("JSESSIONID");Hashtable globalTable = findTableStoringSessions();Hashtable sInfo = (Hashtable) globalTable.get(sID);

// sInfo contains the data related to user

Cookie: JSESSIONID=1239865610;

1239865610

Credit: cs193i at Standford

Example : Online Book Store

using cookiesnetBeans project -CookieSessionEx