Metadata Annotations

An annotation consists of the @ sign preceding the annotation type, followed by a parenthesized list of element-value pairs. The EJB 3.0 Specification defines a variety of annotation types such as those that specify a bean's type (@Stateless, @Stateful, @MessageDriven, @Entity), whether a bean is remotely or locally accessible (@Remote, @Local), transaction attributes (@TransactionAttribute), and security and method permissions (@MethodPermissions, @Unchecked, @SecurityRoles).

Annotations for the EJB 3.0 annotation types generate interfaces required by the class as well as references to objects in the environment. In many cases, defaults can be used instead of explicit metadata annotation elements. In these cases, a developer doesn't have to completely specify a metadata annotation to obtain the same result as if the annotation was fully specified. For example, by default, an entity bean (annotated by @Entity) has a default entity type of CMP, indicating that it has container-managed persistence. These defaults can make annotating enterprise beans very simple. In fact, in many cases, defaults are assumed when an annotation is not specified. In those cases, the defaults represent the most common specifications. For example, container-managed transaction demarcation (where the container, as opposed to the bean, manages the commitment or rollback of a unit of work to a database) is assumed for an enterprise bean if no annotation is specified. These defaults illustrate the "coding by exception" approach that guides EJB 3.0 technology. The intent is to simplify things for developers by forcing them to code things only where defaults are not adequate.