The Java EE 6 Tutorial, Volume I

Helper Classes

The CartBean session bean has two helper classes: BookException and IdVerifier. The BookException is thrown by the removeBook method, and the IdVerifier validates the customerId in one of the create methods. Helper classes may reside in an EJB JAR file that contains the enterprise bean class, a WAR file if the enterprise bean is packaged within a WAR, or in an EAR that contains an EJB JAR or a WAR file that contains an enterprise bean.