pippin
· Pippin, was a Hobbit of the Shire, and one of Frodo Baggins' youngest, but closest friends. He was a member of the Fellowship of the Ring and later became the thirty-second Thain of the Shire
Download JD-GUI to open JAR file and explore Java source code file (.class .java)
Click menu "File → Open File..." or just drag-and-drop the JAR file in the JD-GUI window simple-spring-boot-starter-1.0.0.RELEASE.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.