java.sql.SQLException: Operation not allowed after ResultSet closed

 究根溯源，问题出现在  一个 Statement 对象必须只对应一个 ResultSet 对象，而且在 ResultSet对象执行完一个操作的时候，就会关闭 ResultSet。

            Statement sta2 = conn.createStatement();
            ResultSet res2 = sta2.executeQuery("SELECT * FROM t_customer");
            res2 = sta2.executeQuery("SELECT * FROM t_customer");