asked on

Session Tracking

Hellow Experts,
1. I need stepwise explanation of session tracking like
when user request ,it creates session object ......(I dont need code).
2.Why in System.out.println() out is not initialized to null?
Plz give answers to these simple questions?
Thanks,
Karan

bloodredsun

1./A session is created for the user by the container unlesss you have configured your server not to. The session infomation is kept on the server but the session id (the number representing the session) is passed as a cookie or wirtten as prt of the URL

2./It is an integral part of the System object (see here http://java.sun.com/j2se/1.4.2/docs/api/java/lang/System.html) and cannot be instantiated and therefore initialized.

girionis

For 2) just to add that the "out" stream, i.e. the output stream is static and already open, therefore it does not need any initialization to null.

Manish

ASKER

So for next request session object extract sessionId from
cookie/url ?
session object automatically send sessionId to store in cookie/url?

Manish

ASKER

Why System can not be instantiated?

ASKER CERTIFIED SOLUTION

girionis

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girionis

> So for next request session object extract sessionId from cookie/url ?

No, the server extracts the session id from the cokkie/url.

> session object automatically send sessionId to store in cookie/url?

No, the server stores the session id in a cookie/url.

Manish

ASKER

Thanks girionis,
I just to want to clear abt System class,
System class is not static ,so y it is not instantiated?
and is it correct that out is not initialized to null bec
the output stream is static and already open,.

girionis

Yes, System is not a static (it is final, for more info on final classes have a look here: http://java.sun.com/docs/books/tutorial/java/javaOO/final.html) but you do not instantiate it because all of its methods are static and therefore you can call them straight aways (without having a referebnce to the System class, since as we said static methods belong to the class and not to each individual instance). Besides the constructor for the System class is private (I think) and even if you wanted you couldn't instantiate it.

> and is it correct that out is not initialized to null bec
>the output stream is static and already open,.

To the best of my knowledge this is correct.

Manish

ASKER

Thanks
karan

bloodredsun

Correct, you can't instantiate System and the static members such as out and in are already available for use by the JVM

girionis

Thank you for accepting, glad I was of help :)