Licencheck
· Licencheck is a Java Library that allows 3rd programs to check the validity of a Product License Serial acquired in a Licensoft-web with a simple method.
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 licencheck-2.0.2.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.