JSBML
· JSBML is a community-driven project to create a free, open-source, pure Java library for reading, writing, and manipulating SBML files and data streams.
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 jsbml-1.6.1.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.