初学者问个应该很简单的问题

<?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>
<package name="user" namespace="/" extends="struts-default">
<action name="login" class="com.action.LoginAction">
<result name="success">/index.jsp</result>
</action>
</package>
</struts>
就上面这段代码会出 Content is not allowed in prolog.这个问题，怎么办。