Session Tracking 2 Lec 32 Last Lecture Review

Session Tracking - 2 Lec 32

Last Lecture Review p Session Tracking – why? p Need to store state – typical solutions n n n Cookies – already learned URL Rewriting Hidden Form Fields

Session Tracking Request Session ID = 123 XYZ Amazon Shopping Cart sc [item 1=324] Servlet Container Credit: cs 193 i at Standford

Session Tracking Session ID = 123 XYZ Amazon Shopping Cart sc [item 1=324] Response: Set-Cookie: sid=123 XYZ Servlet Container Credit: cs 193 i at Standford

Session Tracking Request: Set-Cookie: sid=123 XYZ Session ID = 123 XYZ Amazon Shopping Cart sc [item 1=324] Servlet Container Credit: cs 193 i at Standford

Session Tracking Request: Set-Cookie: sid=123 XYZ Session ID = 123 XYZ Amazon Shopping Cart sc [item 1=324 item 2=115] Servlet Container Credit: cs 193 i at Standford

URL Rewriting

URL Rewriting p We can pass extra information to client by rewriting URLs. (appending info with URL) p The extra information can be in the form of p n Extra path information, n Added parameters, or n Some custom, server-specific URL change Due to limited space available in rewriting a URL, the extra information is usually limited to a unique session ID

URL Rewriting: Examples p For example, the following URLs have been rewritten to pass the session id 123 n Original http: //server: port/servlet/rewrite n Extra path information http: //server: port/servlet/rewrite/123 n Added parameter http: //server: port/servlet/rewrite? id=123 n Custom change http: //server: port/servlet/rewrite; $id$123

URL Rewriting: Disadvantages p What if the user bookmarks the page? p Every URL on a page which needs the session information must be rewritten each time page is served n Computationally expensive n Can increase communication overhead p State stored in URLs is not persistent p Limits the client’s interaction with the server to HTTP GET request

Hidden Form Fields

Hidden Form Fields p <input type=“hidden” name=“sessionid” value=“ 123”>

Java’s Solution for Session Tracking Http. Session API

Using Http. Session 1. To get the user’s session object n Call get. Session( ) method of HTTPServlet. Request class n pass false to the get. Session() method Http. Session ses = request. get. Session(false); n If no current session exists: p You will get a null object

Using Http. Session cont. 1. To get the user’s session object (cont. ) n n If true is passed to the get. Session() method then If user already has a session p the existing session is returned For example: Http. Session ses = request. get. Session(true); If no session exists p a new one is created and returned

Using Http. Session cont. 2. Storing information in a session n Session objects works like a Hash. Map p Hash. Map is able to store any type of java object n You can therefore store any number of keys and their values n For example ses. set. Attribute(“id”, “ 123”); key Value

Using Http. Session cont. 3. Looking up information associated with a session String s. ID = (String)ses. get. Attribute(“id”); returns an Object type, so you will need to perform a type cast

Using Http. Session cont. Terminating session 4. n Automatic p n After the amount of time session gets terminated automatically( get. Max. Inactive. Interval( ) ) Manual ses. invalidate();

Example Code Showing Session Information

Encoding URLs Sent to Client Http. Servlet. Response provides two methods to perform encoding p 1. String encode. URL(String URL) 2. String encode. Redirect. URL(String URL) If Cookies disabled p n Both methods encodes (rewrites) the specified URL to include the session ID and returns the new URL If Cookies enabled p n Returns the URL unchanged

Encoding URLs Sent to Client cont. 1. String encode. URL(String URL) n For example String URL = “/servlet/sessiontracker”; String e. URL = response. encode. URL(URL); out. println("<A HREF="" + e. URL + "">. . . </A>");

Encoding URLs Sent to Client cont. 2. String encode. Redirect. URL(String URL) n For example String URL = “/servlet/sessiontracker”; String e. URL = response. encode. Redirect. URL(URL); response. send. Redirect(e. URL);

Example Code Online Book Store