You tried to put an object into your session which isn't serializable. That isn't allowed because the
Tomcat code may need to write the contents of your session to some external location for various reasons.
And it appears that you tried to put a
JDBC connection (or rather, the connection from a connection pool) into your session. Why did you do that? You shouldn't hang onto a session for any longer than a single request, and there's no point in doing so. Just get a connection from the pool every time you need one.