将 doctype 声明添加到您的 struts.xml 文件中.

Add doctype declaration to your struts.xml file.

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
   "-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"
   "http://struts.apache.org/dtds/struts-2.3.dtd">

<struts>
  ...
</struts>