jetbrick-orm/src/main/java/jetbrick/dao/orm/tx/JdbcNestedTransaction.java
@Override
    public void rollback() {
        try {
            if (conn.isClosed()) {
                throw new TransactionException("the connection is closed in transaction.");
            }
            conn.rollback(savepoint);
        } catch (SQLException e) {
            throw new TransactionException(e);
        }
    }
@Override
    public void rollback() {
        try {
            if (conn.isClosed()) {
                throw new TransactionException("the connection is closed in transaction.");
            }
            conn.rollback(savepoint);
        } catch (SQLException e) {
            throw new TransactionException(e);
        }
    }
回滚一个事务