struts2中chain定义问题

<?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>
    <constant name="struts.ui.theme" value="simple" />
    <constant name="struts.devMode" value="true" />
    <constant name="struts.server.static.browserCache" value="false" />
    <package name="myPackage" extends="struts-default">
        <action name="indexAction" class="IndexAction" method="execute">
            <result name="success">index.jsp</result>
            <result name="addPage">WEB-INF/jsp/add.jsp</result>
            <!-- 下面开始报错 -->
            <result name="updatePage" type="chain">
                <param name="actionName">updateAction</param>
                <param name="method">init</param>
                <param name="namespace">/</param>
            </result>
            <!-- 一直到这里 -->
        </action>
        <action name="addAction" class="AddAction" method="add">
            <result name="success">WEB-INF/jsp/add_success.jsp</result>
            <result name="error">WEB-INF/jsp/add_error.jsp</result>
            <result name="input">WEB-INF/jsp/add.jsp</result>
        </action>
        <action name="updateAction" class="UpdateAction" method="update">
            <result name="success">WEB-INF/jsp/update_success.jsp</result>
            <result name="error">WEB-INF/jsp/update_error.jsp</result>
            <result name="input">WEB-INF/jsp/update.jsp</result>
        </action>
    </package>
</struts>