web 应用，在web.xml中配置servlet filter报错

Question

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN" "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd"><web-app id="WebApp_ID"><display-name>servyou</display-name>    <filter>  <filter-name>login</filter-name>  <filter-class>servlet.servletfilter</filter-class>  </filter>    <filter-mapping>   <filter-name>login</filter-name>   <url-pattern>task.jsp</url-pattern>  </filter-mapping>  <servlet>    <servlet-name>Ser</servlet-name>    <display-name>This is the display name of my J2EE component</display-name>    <description>This is the description of my J2EE component</description>    <servlet-class>servlet.Ser</servlet-class>  </servlet>   <servlet-name>Ser</servlet-name>    <url-pattern>/login</url-pattern>  </servlet-mapping>  <servlet-mapping>     <welcome-file-list>   <welcome-file>index.html</welcome-file>   <welcome-file>index.htm</welcome-file>   <welcome-file>login.jsp</welcome-file>   <welcome-file>default.html</welcome-file>   <welcome-file>default.htm</welcome-file>   <welcome-file>default.jsp</welcome-file>  </welcome-file-list></web-app>如果不增加filter的配置就正确，但是一添加就报错，报错信息为The content of element type "web-app" must match "(icon?,display- name?,description?,distributable?,context-param*,servlet*,servlet-mapping*,session-config?,mime- mapping*,welcome-file-list?,error-page*,taglib*,resource-ref*,security-constraint*,login- config?,security-role*,env-entry*,ejb-ref*)".

Answer 1

<servlet-name>Ser</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
  <servlet-mapping>

你这里顺序错乱了，注意xml标签的开闭