Java Persistence API 2.0
· This feature enables support for applications that use application-managed and container-managed JPA written to the Java Persistence API 2.0 specification. The support is built on top of Apache OpenJPA with extensions to support the container-managed programming model.
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-2.0-23.0.0.8.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.