Sams Teach Yourself J2EE™ in 21 Days, Second Edition

Gotchas

The following is a quick checklist of “gotchas” to help you with your implementation:

• Primary keys must be immutable. In other words, it is not possible to change the value of a primary key for an entity once assigned.

• Sometimes, Entity beans interact with non-data store resources such as a subscription to a JMS topic (covered on Day 9, “Java Message Service,” and Day 10, “Message-Driven Beans”). These resources should be acquired in setEntityContext() and released in ejbPassivate() and re-acquired in ejbActivate(). Resources should also be released in unsetEntityContext().

• Finder methods can return a Collection, but they can't currently return a List, Set, or Map object.

• If you have two bean references, note that the value of bean1.equals(bean2) ...