ssh action中service无法注入，报空指针问题

action为：
public class RegistAction {
private IRegistService iregistService;
private SshUser sshUser;
public String registUser(){

System.out.println("=========>"+iregistService);
iregistService.registUser(sshUser);
return "success";
}

struts配置为：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">
<struts>

<!--  <include file="struts-default.xml"></include> -->

<!-- 这句话是将struts交给spring管理 -->
<constant name="struts.objectFactory" value="spring"></constant>

<package name="sshTestPackage" extends="struts-default" namespace="/">
<action name="registAction" class="registAction" method="registUser">
<result name="success">/hello.html</result>
</action>
</package>
</struts>

action里面的service无法注入的原因，就是struts未交付spring托管，
<constant name="struts.objectFactory" value="spring"></constant>的作用就是将struts交付spring托管，同时，action的class必须改为spring配置文件中action的id名