Hi,
In the project I'm involved in, we are using Beans and JSPs. Some of these
beans (*session* beans) have temporarily written information to a database.
We want this change to become permanent *only* once the user has confirmed
and has logged out properly.
However, we need the following feature too:
If a session times out (due to user inaction for too long), we wish to
remove that temporary information from the database. So we need to to have
a way to tell those Beans "hey, the session terminated, so please go and
remove that information from the database".
Our solution: what we are doing (and currently it seems to work) is:
Let those beans implement HttpSessionBindingListener. Then, when the
session ends for any reason, each bean gets unbound and hence receives a
HttpSessionBindingEvent, and so each bean's valueUnbound() method gets
called (and in here we put code to do whatever restoration of the database
if neccessary).
This does seem to work.
However, we are somewhat anxious about the following possiblity:
*Before* our valueUnbound methods finish executing, might not the servlet
engine happen to do garbage collection, thus causing the bean to get
destroyed?
This seems a fair possiblity, because, the way I understand Java
architecture, the instant the session ends, the beans that were bound to
that session are now fair game for garbage collection; i.e., from this point
of time onwards, we do not have any guarantee about the existence of these
beans. So anytime the Java environment wants to, it has the right to kill
any of these beans. Maybe 1 milisecond or 1 hour later, we don't know, but
anytime it can be done...
If that is correct, that means that sometimes the Listeners etc that we are
using; well, sometimes the bean might get destroyed before it has time to
finish restoring the database.
Perhaps the official JSP or Servlet specification says something about this?
However I have not found the information I need. Hope someone can help us!
Thanks in advance,
Sohan Fernando
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