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 shaded-remoteapis-java-2.3.0-M1-52317e00d8d4c37fa778c628485d220fb68a8d08.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.