What is Catalina used for under tomcat\work\?

The file under Tomcat Catalina
is generated after tomcat compiles your project,
that is, the class file of your project (if it is not a java file, copy it directly, such as jsp, etc.)

That is to say, you put the original file of the project in Enter webapps. When tomcat starts, it will compile the projects in
this folder, and then store them in the Catalina directory.

When others access, they will access the files here.
When the user accesses a jsp page for the first time The corresponding page under webapps will be placed under Catalina as a cache reply

. There is a localhost folder under Catalina, mainly because tomcat puts the servlet generated by jsp in this directory. The folder name inside is the name of your project.