code: public static void register() throws SQLException {
      if (isRegistered()) {
        throw new IllegalStateException(
            "Driver is already registered. It can only be registered once.");
      }
      CloudSpannerDriver registeredDriver = new CloudSpannerDriver();
      DriverManager.registerDriver(registeredDriver);
      CloudSpannerDriver.registeredDriver = registeredDriver;
    }
docs: Register the driver against {@link DriverManager}. This is done automatically when the class is
  loaded. Dropping the driver from DriverManager's list is possible using {@link #deregister()}
  method.
  
  @throws IllegalStateException if the driver is already registered
  @throws SQLException if registering the driver fails