Generación de dataset

import com.mysql.jdbc.Connection;
import entities.Rating;
import entities.User;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import util.Query;

public class DataSetFromUser {
    public static void main(String[] args) {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/database_name","user","pass");
            System.out.println("Conexion con la base de datos exitosa");
            Statement stmt = con.createStatement();
            Query queries = new Query(stmt);
            List<User> users = queries.getNHigherRatingsUsers(50);
            int i = 1;
            for(User user : users){
                System.out.println("Guardando los eventos del experimento "+i);
                user.setFrontier(40, 1000);
                List<Rating> events = queries.getRatingPerUserFrontier(user.getFrontierAsString());
                printCSVFile(events, user.getId(), i);
                i++;
            }
        }
        catch (ClassNotFoundException | SQLException ex) {
            System.out.println("Ha ocurrido un error: "+ex.getLocalizedMessage());
            Logger.getLogger(DataSetFromUser.class.getName()).log(Level.SEVERE, null, ex);
        }

    }

    public static void printCSVFile(List<Rating> events, long user_id, int nro_exp){
        StringBuilder sb = new StringBuilder();
        for(Rating event : events){
            sb.append(event.getUser_id());
            sb.append(",");
            sb.append(event.getVenue_id());
            sb.append(",");
            sb.append(event.getRating());
            sb.append("\n");
        }
        try (PrintWriter pw = new PrintWriter(new File(String.format("%05d", nro_exp)+"-rf-data-"+user_id+".csv"))) {
            pw.write(sb.toString());
            pw.close();
        } catch (FileNotFoundException ex) {
            System.out.println("Ha ocurrido un error: "+ex.getLocalizedMessage());
            Logger.getLogger(DataSetFromUser.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}