I was in the process of thinking about @Stateless and JPA and
Serializable (needed some examples for my book...) and noticed that
actually one of the GoF patterns siltently died. Or at least its
realization/implementation has been completely refactored. The Marker Interface
pattern was used to enhance a class with an additional type to change its
behavior or introduce some priviliged actions. Prominent examples are java.io.Serializable
interfaces. Both were introduced because of security reasons. Only
classes which implement those interfaces are able to be flushed to disc or transfered over the network.
With the advent of
annotations, the approach whereby you implement an interface is actually no longer appropriate. The usage of annotations @Serializable or @Remote is much more elegant. There is an example of this in JSR-181, where an endpoint has only to be annotated with the @WebServce annotation. No additional interface realization/implementation is necessary.
an annotation is not the same as implementing an interface, because the
type of the class is not going to be extended. Nonetheless, the same
effect can be achieved. So, the infrastructure no longer needs to check the
type (e.g., with instanceof), but has to check the existence of the annotation via reflection (class#getAnnotation or isAnnotationPresent) instead.
So java.io.Serializable and java.rmi.Remote are actually legacy now!
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