[求助]SOS咯 关于注入问题

我将LoginDAO注入相应的Service中.只有在启动服务时能注入,以后DAO在Service类就无法再注入了.WHY?麻烦知道的大侠指导下.先XX了
<!-- to create a LoginDAO instance -->
<bean id="loginObj" class="cq.training.dao.LoginDAO">
<property name="sessionFactory">
<ref bean="sessionFactory"/>
</property>
</bean>

<!-- -->

<!-- to create the loginService instance -->
<bean id="loginService" class="cq.training.service.LoginService">
<property name="loginDAO">
<ref bean="loginObj"/>
</property>
</bean>