IBM FHIR Server
· The IBM® FHIR® Server is a modular Java implementation of version 4 of the HL7 FHIR specification with a focus on performance and configurability.
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 fhir-parent-4.11.1.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.