Cannot upgrade/downgrade to Dynamic Web Module 2.3 facet

<!DOCTYPE web-app PUBLIC   "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"   "http://java.sun.com/dtd/web-app_2_3.dtd" >    <web-app>    <display-name>Archetype Created Web Application</display-name>  </web-app>  

<?xml version="1.0" encoding="UTF-8"?>  <web-app version="2.5"      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_2_5.xsd">          <display-name>Archetype Created Web Application</display-name>  </web-app>  

http://blog.csdn.net/steveguoshao/article/details/38414145

web.xml 里面定义了当前  Dynamic Web Module，需要更改