Oracle has changed some of the behavior of its JDBC driver for 12c. If autocommit is enabled and an explicit commit is execute, it blows up.
java.sql.SQLException: Could not commit with auto-commit set on
OK, fair enough - it doesn't make sense to commit with auto-commit on. Comments I've read state that the JDBC spec demands this behavior, and Oracle is finally catching up. The earlier JDBC drivers don't throw this error. I don't believe any other JDBC drivers (MS, etc.) throw this error!
Our application needs to be fixed now.