Another feature that the Enterprise Server provides is the read-only bean, an entity bean that is never modified by an EJB client. Read-only beans avoid database updates completely.
Read-only beans are specific to the Enterprise Server and are not part of the Enterprise JavaBeans Specification, v2.1. Use of this feature for an EJB 2.1 bean results in a non-portable application.
A read-only bean can be used to cache a database entry that is frequently accessed but rarely updated (externally by other beans). When the data that is cached by a read-only bean is updated by another bean, the read-only bean can be notified to refresh its cached data.
The Enterprise Server provides a number of ways by which a read-only bean’s state can be refreshed. By setting the refresh-period-in-seconds element in the sun-ejb-jar.xml file and the trans-attribute element (or @TransactionAttribute annotation) in the ejb-jar.xml file, it is easy to configure a read-only bean that is one of the following:
Access to CMR fields of read-only beans is not supported. Deployment will succeed, but an exception will be thrown at runtime if a get or set method is invoked.
Read-only beans are best suited for situations where the underlying data never changes, or changes infrequently. For further information and usage guidelines, see Using Read-Only Beans.