Thanks vahan...
but it doesn't work!!!
I've the same error!
Now i've used,following you
package giu;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.http.HttpSession;
import javax.sql.DataSource;

public class QueryManager extends BaseBean{
    private int key;

    public QueryManager(){}

public String executeTransaction() throws java.sql.SQLException {
   java.sql.Connection conn = null;
   javax.sql.DataSource dataSource =
Singleton.getInstance().getDataSource();
   conn = dataSource.getConnection();

   Experiment exp = (Experiment) ViewUtils.eval("#{experiment}");

   List results = new ArrayList();
   ResultSet rs = null;
   Statement stmt = null;
   boolean allgood = false;
   if (conn != null) {

       conn.setAutoCommit(false);
       //you can change Transaction Isolation level

//conn.setTransactionIsolation(java.sql.Connection.TRANSACTION_READ_COMMITT?ED);

       conn.setSavepoint();//set rollback point

       try {
           for (int i = 0; i < exp.getExperiments().size(); i++) {

               ((java.sql.PreparedStatement)
                exp.getExperiments().get(i)).executeUpdate();
               if (i == (exp.getExperiments().size() - 1)) {
                   conn.commit();
               }

           }
       } catch (Exception e) {
               conn.rollback();
               e.printStackTrace();
           }

   } else {
       System.out.println("connessione non disponibile");
   }

   return "submit";
}

}

but never,when sql exception comes rollback doesn't act!
Please help me..should i do other things for support transactions?
I'm using
mysql-connector-java-3.1.13.zip

and innodb table with mysql...what can i do?
Please help me