XMvn
· XMvn is a set of extensions for Apache Maven that can be used to
manage system artifact repository and use it to resolve Maven
artifacts in offline mode. It also provides Maven plugins to help
with creating packages containing Maven artifacts.
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 xmvn-4.2.0.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.