@Autowired原理

例子、

// <bean id="> id默认类名首字母小写 默认是单例
// @Scope(value = "prototype")
@Repository
public class UserDao extends BaseDao<User> {
      @Override
      public void save() {
          System.out.println("UserDao...保存用户....");
      }
}

@Service
public class UserService {

      // 自动装配，自动的为这个属性赋值
      @Autowired
      private UserDao userDao;

      public void save(){
          userDao.save();
      }
 }

@Service
public class UserServiceExt extends UserService {

      @Autowired
      private UserDao userDao;

      @Override
      public void save() {
            System.out.println("userServiceExt.......");
      }
}

  @Controller
  public class UserController {
      // Qualifier:指定一名作为id，让spring别使用变量名作为id
      @Qualifier("userService")
      @Autowired
      private UserService userServiceExt2;

      public void save(){
            userServiceExt2.save();
      }

  }