I implemented a simple algorithm that will select the closest free elevator. If there is no free elevator it will select any elevator that is max 3 floors away. If there is no such elevator the user needs to be put in a queue.
I also created a simple web-gui that can be viewed at localhost:8080 when the app is running. If I had more time I would have implemented this fully, so that users occupy the elevators. Right not it just finds an elevator.
As the project is, the Spring app can be started as seen below.
build and run the code with Maven
mvn package
mvn spring-boot:run
Then go to localhost:8080 to see a simple gui.