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 multiple-dimension-spread-legacy-maker-0.8.11_hive-1.2.1000.2.6.4.0-91.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.