filter-name 报：is not allowed here 异常解决方案，severlet3.0以后的规范不再有 XML 了

<?xml version="1.0" encoding="UTF-8"?>    <!--        <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee         http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"         version="3.1">    -->        <!--  将上面的<web-app> 实例引用模板信息将不会报错  -->        <!--   方法一  -->                            <!--                                     <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"                                     xmlns="http://java.sun.com/xml/ns/javaee"                                     xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"                                     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee                                     http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"                                     id="WebApp_ID" version="2.5">                             -->        <!--   方法二  -->                                    <web-app xmlns="http://java.sun.com/xml/ns/javaee"                                     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"                                     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee                                     http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"                                     version="3.0">        <!--    -->        <filter>            <filter-name>struts2</filter-name>            <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>        </filter>        <filter-mapping>            <filter-name>struts2</filter-name>            <url-pattern>/*</url-pattern>        </filter-mapping></web-app>