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From Veniamin Fichin <3ca28...@mail.ru>
Subject Re: SESSION VARIABLE BECOMES NULL AFTER SOME REFRESH
Date Mon, 12 Apr 2004 11:53:14 GMT
Peter Guyatt wrote:

> Hi There,
> 
> 	The NPE is coming from the { if (session == null || session.isNew()) }
> since even if session is null then you are still trying to call a method of
> session.

    According to Java language specification, "15.24 Conditional-Or 
Operator ||", it's not so. That says that right-hand operator only 
executes when left-hand operator is false, so in this code session!=null.

> -----Original Message-----
> From: MUKUND Premchander [mailto:PMukund@covansys.com]
> Sent: 12 April 2004 11:19
> To: tomcat-user@jakarta.apache.org
> Subject: SESSION VARIABLE BECOMES NULL AFTER SOME REFRESH
> 
> Hi,
> 
> I have a jsp page which is refreshed atuomatically every 10 seconds.I
> get and put values in the session by using the implicit session variable
> . Everything works fine for say 2-3 mins after that the session becomes
> null and throws a null pointer exception.
> 
> IN the try block I even have a code as
> try {
>      if (session == null || session.isNew()) {
>             //do something
>       } else {
>              //do otherwise
>       }
>  }catch(Exception e )
>  { //print stack trace and value of session }
> 
> I get a null pointer exception and session is preinted as null but even
> the if block is noit executed . I printed the value of
> request.getSession(false);.This gives me session object ,where as the
> implicit session does not have this after many refresh interval . During
> the first few refresh both have the same value.

    May be some logic deep in your code invalidates session somehow? You 
can set up RequestDumperFilter to look at HTTP headers you (your 
browser) send and what is received. I don't know if that filter 
available in Tomcat 3.2, 'cause I use it since 4.1 time, but you can 
grab it from recent Tomcat distribution. Or you can use 
javax.servlet.http.HttpSessionListener to be notified when a session is 
about to be invalidated or timed out.

> Also note that this runs fine in Windows ,I get this problem only in
> UNIX . I use tomcat 3.2 in unix and view using IE in windows


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