JDBC and transactions

Hi

I'm trying to figure out how to use transactions with JDBC and PostGresql,
without much success. In particular, I can't figure out how to mark the
start of a transaction and how to do a rollback.

I'm iterating through a list of objects and I insert them into the DB one by
one. However, it is possible to get a NoSuchElement runtime exception while
going through the list. If this happens, I want to rollback all the previous
inserts.

The code/pseudo-code looks like this.

Connection conn = // get the connection
conn.setAutoCommit(false);

boolean rollBack = false;

while(myList.hasNext()) {
    MyObject obj = null;
    try {
        obj = (MyObject)myList.next();
    }
    catch(NoSuchElementException e) {
        rollBack = true;
        break;
    }

    try {
        persistToDB(conn, obj);
    }
    catch(SQLException e) {
        rollBack = true;
        break;
    }
}

if(rollBack) {
    try {
        conn.rollback();
    }
    catch(SQLException e) {}
}
else {
    try {
        conn.commit();
    }
    catch(SQLException e) {}
}

conn.close();


I run this code and, in order to test it, deliberately throw a
NoSuchElementException. My code correctly detects this and calls the
rollback method on the connection. But when I look in the database, the rows
before the exception have been inserted, and the rollback hasn't done
anything. So how do I specify the start of the transaction? I've even tried
executing Statements and PreparedStatements with the query "begin", trying
to emulate the PostGresql "begin" syntax, but this doesn't work either. I
know the syntax of the statements I use to persist the object are good, and
I'm not seeing any exceptions when I do any of the SQL commands. (I ignore
some of the exceptions because these haven't caused my any problems).

Has anybody successfully used the rollback method for a group of SQL
commands using the PostGresql JDBC driver?

Thanks

Ryan