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 pax-logging-sample-fragment-log4j2-h2-2.1.0-wso2v5.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.