@Test

     public void testAddUser() throws Exception {

         ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");//初始化ApplicationContext对象，加载配置文件

         UserService service = (UserService)ctx.getBean("userService");//从容器中取

         UserService service2 = (UserService)ctx.getBean("userService");//从容器中取

         System.out.println(service == service2);//true

         User u = new User();

         u.setUsername("zhangsan");

         u.setPassword("zhangsan");

         service.addUser(u);//容器中已经配置了UserDAOImpl了，并把DAOImpl注入到service之中，所以service直接就可以保存了

     }