在Project Facets里面修改Dynamic web module为3.0的时候就会出现Cannot change version of project facet Dynamic web module to 3.0
解决问题步骤如下：
1.修改web.xml为
<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" ???xmlns="http://java.sun.com/xml/ns/javaee" ???xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" ???id="schedule-console" version="3.0"> ???<display-name>Archetype Created Web Application</display-name></web-app>
注意web-app_3_0和version=3.0
2.打开项目.settings目录下的org.eclipse.wst.common.project.facet.core.xml
?<installed facet="java" version="1.8"/> <!-- java版本1.8 --> ?<installed facet="jst.web" version="3.0"/> <!-- servlet3.0 --> ?<installed facet="wst.jsdt.web" version="1.0"/>
3.maven update
解决Cannot change version of project facet Dynamic web module to 3.0
原文地址：http://www.cnblogs.com/CComma/p/8011462.html