A great UML Generator tool for Eclipse and STS: ObjectAid UML (objecaid.com)
From the site:
The ObjectAid UML Explorer is an agile and lightweight code visualization tool for the Eclipse IDE. It shows your Java source code and libraries in live UML class and sequence diagrams that automatically update as your code changes.
I also like to use a free softare to draw UML diagrams, which is called Umlet.