web.xml是tomcat和spring间的桥梁，是tomcat构建spring运行环境的说明书
It is a web application deployment descriptor file, contains detail description about web application like configuration of Servlet, Session management, Startup parameters, Welcome file..etc.
We can not change the directory or extension name of this web.xml because it is standard name to recognized by container at run-time.
web.xml is present inside the Web-INF folder.
https://www.sitesbay.com/servlet/servlet-web-xml