code: public synchronized void cleanup() {
          if (driver != null) {
              DriverLoader.cleanup(driver);
              driver = null;
          }
          connectionString = null;
          userName = null;
          password = null;
      }
docs: Cleans up resources and unloads any registered database drivers. This
  needs to be called to ensure the driver is unregistered prior to the
  finalize method being called as during shutdown the class loader used to
  load the driver may be unloaded prior to the driver being de-registered.