This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
By composite key class I assume you mean the JPA IdClass?
The IdClass in JPA must match your Entity Id fields. So if you use field access (annotated the fields) then your IdClass only needs the fields, does not need to methods (although your app may still want the methods). If you use property access (annotate the methods), then your IdClass must have those same methods.