spring 对象引用报错??报错

使用spring注解后，引用对象就报错，

@Service("UserBiz")
public class UserBizImpl implements UserBiz{

 @Autowired

 private UserDao userDao;

 public boolean login(UserBean userBean) {
  return userDao.login(userBean);
 }
}

xml中如下配置

<bean id="userBiz" class="com.szy.biz.impl.UserBizImpl">
    <property name="userDao" ref="userDao"></property>

</bean>
<!--指定登录的实现bean  -->
<bean id="userDao" class="com.szy.dao.impl.Test"></bean>

这样配置后就报org.springframework.beans.NotWritablePropertyException: Invalid property 'userDao' of bean class [com.szy.biz.impl.UserBizImpl]: Bean property 'userDao' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?

如果我将<property》去掉

 <bean id="userBiz" class="com.szy.biz.impl.UserBizImpl">
 <bean id="userDao" class="com.szy.dao.impl.Test"></bean>

运行正常，求解?