public static boolean userExist(String email){
        SQLiteJDBC db = new SQLiteJDBC();
        String sql = String.format("SELECT user_id FROM users WHERE email='%s'", email);
        ResultSet resultSet = db.query(sql);
        
        try {          
            if(resultSet.next())
                return true;
            
            db.close();
        }catch(Exception e) {
            System.err.println( e.getClass().getName() + ": " + e.getMessage() );
            System.exit(0);
        } 
        return false;
    }