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 org.eclipse.jgit-parent-6.3.0.202209071007-openl-2.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.