明明有值却显示NullPointerException

报错:
Exception in thread "main" java.lang.NullPointerException
at rss.SendMailFromSina.save(SendMailFromSina.java:27)
程序代码:
package rss;

import aop.AopPort;
import pojo.User;
import dao.UserDAO;

public class SendMailFromSina implements SendMail{
public void sendMail(){

System.out.println(save());
System.out.println("SEND MAIL!!!");
}

private String save(){
/*OrderDAO od = new OrderDAO();
Order o = new Order();
o.setOrderid(0);
o.setOrdername("a");
o.setUserid(0);
od.save(o);*/
UserDAO ud = (UserDAO) new AopPort().getAopBeans("UserDAO");
User u = new User();
u.setUserId(8);
u.setUserName("i");
ud.save(u);
return "save";
}


}