how to get a service bean in action class?

struts-config.xml

<plug-in
className="org.springframework.web.struts.ContextLoaderPlugIn">
<set-property property="contextConfigLocation"
value="ext-spring-actions.xml" />
</plug-in>


ext-spring-actions.xml

<beans>
<bean name="/spr/user/view_user" class="com.user.action.UserAction">
<property name="userManager" ref="userManager"/>
</bean>
</beans>

ext-spring.xml

<bean id="userManager" class="com.user.impl.UserManager">
<property name="dao" ref="dao"> </property>
</bean>

UserAction:

public class UserAction extends PortletAction {

private IUserManager userManager;

public IUserManager getUserManager() {
return userManager;
}
public void setUserManager(IUserManager userManager) {
this.userManager = userManager;
}

public ActionForward render(
ActionMapping mapping, ActionForm form, PortletConfig portletConfig,
RenderRequest renderRequest, RenderResponse renderResponse)
throws Exception {

System.out.println("user test is successed" + this.getUserManager());

return mapping.findForward("portlet.spr.user.view");
}

}

but the result is null
this.getUserManager() is null?

why???

who can tell me?