Why set a JSP page session = "false" directive?

Question

I was wondering when you would want to set the following page directive in a JSP:

<%@ page session="false" %>

I know that it prevents the creation of the session object, but when would you need to do that? Is it considered a best practice when a JSP does not need to access the implicit session?

NOTE: The reason why I ask, is because it was in this Spring MVC tutorial and I assume the springsource folks know their stuff - http://blog.springsource.com/2011/01/04/green-beans-getting-started-with-spring-mvc/

Answer 1

One reason would be performance and memory. If you have a page that doesn't need to be involved in a session (like say, an about.jsp or faq.jsp) then the default behaviour of involving every JSP in a session will impose the overhead of creating a new session object (if one doesn't already exist) and increased memory usage as more objects reside on the heap.

This effect will be greatly exaggerated in case of a single page seeing high traffic from many unique users combined with a high bounce rate i.e. they users do not continue to browse but leave the site immediately after viewing that one page- the container will create a new session object per user which will never be used again and will ultimately be garbage collected after it times out - added over head of object creation, memory usage and garbage collection without giving you any real value.