How are you testing that the connections aren't released?
The file you posted looks like a hibernate configuration file. Is that right? If yes, how are you using Hibernate in your application?
Are you setting up the entitymanagers yourself
What command do you use to start the server and please post the entire exception stacktrace that you see after copying that driver jar to that location.
This snippet means there needs to be a setSelectedSubjects(List<Integer>) method in your UpdateStudentInfoBean class. I cannot see such a method.
There is a method called setSelectedSubjectsInfo(List<Integer>). Should this be renamed to setSelectedSubjects?