| = CDI Events - Loose Coupling and Extensibility |
| :index-group: CDI |
| :jbake-type: page |
| :jbake-status: published |
| |
| CDI allows you to extend business code by the Notifier/Observer pattern. |
| |
| To do it you simply inject a field `Event` in the notifier class. This class is a template |
| and the parameter type is the object type to fire. Then when you want to notify observers |
| you simply call the method fire of the event object passing as a parameter the event itself |
| (your own class!). |
| |
| On the other side you annotated a method parameter `@Observes` and the parameter type is the sent type |
| by the notifier. |
| |
| NOTE: of course you can add qualifiers to be more precise on your events. |
| |
| == Example |
| |
| The example is pretty simple: an ejb uses the `@Schedule` annotation to get a notification each second. |
| The each second this EJB will send the current date through CDI events. |
| |
| This is our "business" code. It is a simple behavior (nothing). |
| |
| In our test (which is considered as an extension) we created an observer (`Observer` class) |
| which simply store and log each received date. |
| |
| The test itself (`EventTest`) simply verifies the dates were received. |
| |
| == Conclusion |
| |
| CDI let's you implement very easily plugins through this event mecanism. |
| |
| If you go further and look at CDI plugin API you'll realize it is simply the same kind |
| of events. CDI events is really the basis of CDI. |
