The J2EE™ Tutorial Second Edition

Primary Keys for Container-Managed Persistence

Sometimes you must implement the class and package it along with the entity bean. For example, if your entity bean requires a composite primary key (which is made up of multiple fields) or if a primary key field is a Java programming language primitive type, then you must provide a customized primary key class.

The Primary Key Class

For container-managed persistence, a primary key class must meet the following requirements:

• The access control modifier of the class must be public.

• All fields must be declared as public.

• The fields must be a subset of the bean's persistent fields.

• The class must have a public default constructor.

• The class must implement the hashCode() and equals(Object other) methods. ...