A WEB-INF is the security directory of Java WEB applications. The so-called security is a directory that the client cannot access, but only the server can access.
The second web.xml is the project deployment file.
How to set welcome page
<welcome-file-list>
<welcome>/haha.jsp</welcome>
</welcome-file-list>
Three classes folder, used to place *.class files.
Four lib folders are used to store the required jar packages.