Optional Annotations
In addition to those defined in JSR 250, the following annotations MAY be handled by the container.
@Async
Indicates that a method call could actually be performed asynchronously in the background using a proxy of some kind to avoid blocking the calling thread.
@Singleton
Allow POJOs to be marked as being singletons so that an IoC container does not create multiple instances of them.
@OptionalResource
Used to mark a property or field as optional; but also allow indication of the name you'd like to use in JNDI to look it up if it is available.