Could not resolve XML resource [null] with public ID [-//Sun Microsystems, Inc.//DTD Web Application

创建项目时自动生成的web.xml配置文件头，是2.3的，改成2.5以及以上版本需要更换格式成：

<?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_1.xsd" version="3.1">

报错：web-app必须在一个实体内；多余的<web-app>标签

Could not resolve XML resource [null] with public ID [-//Sun Microsystems, Inc.//DTD Web Application

原文：https://www.cnblogs.com/agnesFlower/p/12009790.html