Tomcat uploads files to a temporary file directory, and you can override where that directory is located. People usually don't, however. There are no explicit changes that need to be made to Tomcat to support file uploads - it works fine "straight out of the box".
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.