Transaction doesn't rollback

Question

Hello guys,
I 've a trouble and I'm not able to solve it..Ineed your help...
I have a jsf application.
I need to execute several insert query into a mysql db in a transaction, so operation must be accomplished only if all query are successfully executed.
To solve this issue I thinked to store prepared statement into an arraylist and passing it to a method that execute queries...if at least one query gives exception transaction must be rollback.
So in my code I've
ArrayList list = new ArrayList(); //collects prepared statements
PreparedStatement ps= conn.prepareStatement(....);
list.add(ps);
String result= Helper.executeTransaction(list);//I call static method to execute queries in transaction.Issue is that if a query fails during execution, exception is thrown but transaction is not rollback..so queries that has been successfully executed write into db...
This is method to execute transaction...
public static String executeTransaction(ArrayList ps) {
        Connection conn = null;
        String result = "success";
        String allgood = "false";
        try {
            conn = Singleton.getInstance().getInstance().getDataSource().getConnection();
        } catch (SQLException ex) {
            Logger.getLogger(Helper.class.getName()).log(Level.SEVERE, null, ex);
        List results = new ArrayList();
        try {
            conn.setAutoCommit(false);
        } catch (SQLException ex) {
            Logger.getLogger(Helper.class.getName()).log(Level.SEVERE, null, ex);
        for (int i = 0; i < ps.size(); i++) {
            try {
                int nrows = ((java.sql.PreparedStatement) ps.get(i)).executeUpdate();
                allgood = "true";
                results.add(allgood);
            } catch (Exception z) {
                z.printStackTrace();
                allgood = "false";
                results.add(allgood);
        for (int j = 0; j < results.size(); j++) {
            if ((results.get(j)).equals("false")) {
                try {
                    conn.rollback();
                } catch (SQLException ex) {
                    Logger.getLogger(Helper.class.getName()).log(Level.SEVERE, null, ex);
            result = "failure";
            return result;
        try {
            conn.commit();
        } catch (SQLException ex) {
            Logger.getLogger(Helper.class.getName()).log(Level.SEVERE, null, ex);
        return result;
    }Debugging code seems like system arrives to conn.rollback(), but it seems like after executing correctly query data are written in the db without waiting for other queries, to estabilish if commit or rollback.
Where is the error?
Please help me

Answer 1

Hello guys,
thanks for your replies...
but issue isn't still clear to me...
Please correct me if I'm wrong.
Basing on what I understood from your answers I evaluated my code but I'm not able what I miss..
I set
conn.setAutoCommit(false);that mean that data are not entered into db before commit is run..
I stored all prepared statement in a list (and I think it's ok)..I iterate on list executing prepared statement and I store a boolean for each query execution (why data are entered into db if I set conn.setAutoCommit(false)?
Next I read list of boolean, if I find a "FALSE" I run
conn.rollback();
It seems correct to me...could you help me with my code?
Or at least more explanation...
Thanks