action中调用service层，service层中通过spring的依赖注入dao,但在调用的时候发现空指针异常，
发现dao为空，请问原因在哪？哪位高手指教
配置如下：配置放两个配置文件中的：
applicationcontext-service.xml:
<bean id="userManager" class="org.opensource.service.impl.UserManagerImpl">
        <property name="userDao" ref="userDao"/>
</bean>
applicationcontext-hibernate.xml:
<bean id="roleDao" class="org.opensource.dao.hibernate.RoleDaoHibernate">
    <property name="sessionFactory" ref="sessionFactory"/>
</bean>

public class RoleManagerImpl extends BaseManager implements RoleManager{
    private RoleDao dao;
    public Role getRole(String rolename) {
        // TODO Auto-generated method stub
        return dao.getRoleByName(rolename);／／空指针异常处，dao为空
    }
    public void setRoleDao(RoleDao roleDao) {
        // TODO Auto-generated method stub
        this.dao=dao;
    }
｝

service中的配置贴错了，应该是下面这个
    <bean id="roleManager" class="org.opensource.service.impl.RoleManagerImpl">
        <property name="roleDao" ref="roleDao"/>
    </bean>

private RoleDao dao属性要有set方法 才能注入