This SDK is announced to be deprecated latest by 31 December 2022, please follow more details on SDK deprecation plan https://docs.commercetools.com/api/releases/2021-08-31-announced-long-term-support-plan-for-commercetools-sdks. We recommend you to use our new SDK here https://docs.commercetools.com/sdk/jvm-sdk#java-sdk-v2.
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 commercetools-java-client-apache-async-2.14.0.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.