The example we’ll use is a Social media feed processor.
So I have created an interface:
Â
public interface SocialFeedProcessor {
Feed process(String feed);
}
and provided 2 implementations, twitter and google+
Â
public class TwitterFeedProcessor implements SocialFeedProcessor{ @Override public Feed process(String feed) { System.out.println("processing this twitter feed"); // processing logics return new Feed(feed); } }
public class GooglePlusFeedProcessor implements SocialFeedProcessor {
@Override
public Feed process(String feed) {
System.out.println("processing this google+ feed");
// processing logics
return new Feed(feed);
}
}
I’ll annotate these 2 beans by a custom Qualifier as described here
Â
@javax.inject.Qualifier
@java.lang.annotation.Retention(RUNTIME)
@java.lang.annotation.Target({FIELD, PARAMETER, TYPE})
@java.lang.annotation.Documented
public @interface FeedProcessor {
}
and I annotate my 2 processors with it.
Â
@FeedProcessor
public class TwitterFeedProcessor implements SocialFeedProcessor{
@Override
public Feed process(String feed) {
System.out.println("processing this twitter feed");
// processing logics
return new Feed(feed);
}
}
@FeedProcessor
public class GooglePlusFeedProcessor implements SocialFeedProcessor {
@Override
public Feed process(String feed) {
System.out.println("processing this google+ feed");
// processing logics
return new Feed(feed);
}
}
Nothing really special, but now when we write our decorator we use the power of CDI to only decorate the classes with the @FeedProcessor annotation.
Â
@Decorator
public class SocialFeedDecorator implements SocialFeedProcessor {
@Delegate
private @FeedProcessor SocialFeedProcessor processor;
@Override
public Feed process(String feed) {
System.out.println("our decorator is decorating");
return processor.process(feed);
}
}
the only thing that is left is registering our decorator in our beans.xml
Â
<decorators>
<class>be.styledideas.blog.decorator.SocialFeedDecorator</class>
</decorators>
By using the annotation, we automatically decorate all our implementations of the SocialfeedProcessor with this decorator. When we add an extra implementation of the SocialFeedProcessor without the annotation, the bean will not be decorated.
Related Article:
Reference: Java EE6 Decorators, advanced usage from our JCG partner Jelle Victoor at Styled Ideas Blog
