В вашем контексте контекст-слушатель контекстного методаDestroyed () вручную отмените регистрацию драйверов:
// This manually deregisters JDBC driver, which prevents Tomcat 7 from complaining about memory leaks wrto this class
Enumeration<Driver> drivers = DriverManager.getDrivers();
while (drivers.hasMoreElements()) {
Driver driver = drivers.nextElement();
try {
DriverManager.deregisterDriver(driver);
LOG.log(Level.INFO, String.format("deregistering jdbc driver: %s", driver));
} catch (SQLException e) {
LOG.log(Level.SEVERE, String.format("Error deregistering driver %s", driver), e);
}
}