Professor, if you pass an object through a session, the next time the server restarts and the servlet is reloaded, is that object gone?

For instance, when a user accesses my servlet for the first time, he goes through a form to enter firstname, lastname, and age.  Then this Person(firstname, lastname, age) object is added to the session.  If i reload the page, it updates the visitCount.  But if I restart the server and re-implement the servlet, the object becomes null.  Why?

I have attached the code.  Open it with Notepad++

Integers work though, and they are objects.  Strange.

Integer objects do not turn NULL, but the person objects turn NULL.

yea, check out this code.  No matter what I do, the Integer object never turns to NULL they just keep incrementing.

Shows the session information including the visit count.  The visit count always increments, even if I restart the server.  It never turns to 0.

ya

Tomcat tries to preserve live sessions between restarts. This feature is useful when you want to restart the server to load a new version of an application, but there are some users who are currently logged in. By preserving sessions, once the server is restarted, these users don't have to log in again (and hopefully won't notice the service interruption).

The way Tomcat saves session data is to write them to disk. Note that this requires the objects to implement the Serializable interface, which I guess is the reason why Integer was save but not the Person object in your example.