> How can I use the directives

You can use only DSQL in JayBird. All isql directives like SET NAMES,
etc. will not work. You should use JDBC alternatives them.

> - START_TRANSACTION

Not available, there's always a transaction associated with the
connection.

> - ROLLBACK

java.sql.Connection.rollback();

> - COMMIT

java.sql.Connection.commit();