Friday, March 13, 2009

How can I enable session tracking for JSP pages if the browser has

Question :How can I enable session tracking for JSP pages if the browser has

disabled cookies? (JSP)

Answer :We know that session tracking uses cookies by default to associate a

session identifier with a unique user. If the browser does not support

cookies, or if cookies are disabled, you can still enable session tracking

using URL rewriting.

URL rewriting essentially includes the session ID within the link itself as a

name/value pair. However, for this to be effective, you need to append the

session ID for each and every link that is part of your servlet response.

Adding the session ID to a link is greatly simplified by means of of a couple

of methods: response.encodeURL() associates a session ID with a given

URL, and if you are using redirection, response.encodeRedirectURL() can

be used by giving the redirected URL as input.

Both encodeURL() and encodeRedirectedURL() first determine whether

cookies are supported by the browser; if so, the input URL is returned

unchanged since the session ID will be persisted as a cookie.

Consider the following example, in which two JSP files, say hello1.jsp and

hello2.jsp, interact with each other. Basically, we create a new session

within hello1.jsp and place an object within this session. The user can then

traverse to hello2.jsp by clicking on the link present within the page.Within

hello2.jsp, we simply extract the object that was earlier placed in the

session and display its contents. Notice that we invoke the encodeURL()

within hello1.jsp on the link used to invoke hello2.jsp; if cookies are

disabled, the session ID is automatically appended to the URL, allowing

hello2.jsp to still retrieve the session object.

Try this example first with cookies enabled. Then disable cookie support,

restart the brower, and try again. Each time you should see the

maintenance of the session across pages.

Do note that to get this example to work with cookies disabled at the

browser, your JSP engine has to support URL rewriting.


<%@ page session="true" %>


Integer num = new Integer(100);


String url =response.encodeURL("hello2.jsp");




<%@ page session="true" %>


Integer i= (Integer )session.getValue("num");

out.println("Num value in session is "+i.intValue());

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