Thread: Should I use a framework/build tools etc?

Hi!
I've been programming PHP for 15 years and want to learn something new so I've decided to try to do some of my projects at work in Java. My boss doesn't care as long as it gets the job done.
I've managed to compile and run a few programs now but im curious how I should set up my projects and what frameworks and build tools etc to use (if any).

Here are a couple of projects that I want to do. I use the IntelliJ editor and the server which will host the programs has Java 8 runtime - and we are thinking of maybe installing Docker on the machine later for Spring projects.

- A cronjob will trigger a program that fetches files from an ftp server and injects the data into a mysql database.
- A program will convert image files to pdf files and notify users on slack and sms.
- Build a REST microservice which queries a database and returns data as json.
etc

I know how to program the classes to do the actual work, but everything else I have no idea about. Like Maven - i guess it is like the php version of "composer". Is it overkill to use it for these small projects? Are there better alternatives? Should I use Spring Boot? What do modern Java programmers use?

When looking for libraries etc to do PDF processing and FTP stuff, where should I look - is there some "official" repo of quality and well documented libraries?