1、進入專案下的.settings資料夾
開啟org.eclipse.wst.common.project.facet.core.xml

 <?xml version="1.0" encoding="UTF-8"?>  
  <faceted-project>  
    <fixed facet="wst.jsdt.web"/>  
    <installed facet="java" version="1.5"/>  
    <installed facet="jst.web" version="2.3"/>  
    <installed
 
 facet="wst.jsdt.web" version="1.0"/>  
  </faceted-project> 

2、修改內容如下：

<installed facet="jst.web" version="3.1"/>

3、修改專案web.xml的檔案頭，內容如下：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
 

    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    id="WebApp_ID" version="3.1">

    <display-name>Archetype Created Web Application</display-name>
</web-app>