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 jaxb2-m2e-connectors-parent-2.0.0.20120826-0129.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.