在应用下面加 WEB-INF 建 web.xml 内容如下

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app 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_3_0.xsd"
  version="3.0"
  metadata-complete="true">
 
  <display-name>Welcome to Tomcat</display-name>
  <description>
     Welcome to Tomcat
  </description>
    <error-page>
        <error-code>404</error-code>
        <location>/index.html</location>
    </error-page>
</web-app>