Java Persistence API 2.2
· This feature enables support for applications that use application-managed and container-managed JPA. This feature includes Java Persistence API 2.2 specification interfaces and container-managed JPA integration. EclipseLink is also included as the default JPA provider implementation.
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 jpa-2.2-23.0.0.8.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.