# MVC and CDI

In before posts, we have already use `@Inject` to inject CDI beans into the Controller class. In fact, MVC embraced CDI internally.

## RedirectScoped

There is a new CDI compatible scope named `RedirectScoped` introduced in MVC 1.0.

A bean annotated with `@RedirectScoped` annotation can be transferred between two requests, conceptly, it is similar with JSF Flash.

The `AlertMessage` is an example.

1. Declare a bean with `@RedirectScoped` annotation.

   ```java
    @RedirectScoped
    @Named("flashMessage")
    public class AlertMessage implements Serializable {}
   ```
2. Inject it into a Controller class.

   ```java
    @Inject
    AlertMessage flashMessage;
   ```
3. Access the bean properties in the view via EL.

   ```java
    <c:if test="${not empty flashMessage and not empty flashMessage.text}">
        <div class="alert alert-${flashMessage.type} alert-dismissible"
             role="alert">
            <button type="button" class="close" data-dismiss="alert"
                    aria-label="Close">
                <span aria-hidden="true"><![CDATA[&times;]]></span>
            </button>
            <p>${flashMessage.text}</p>
        </div>
    </c:if>
   ```

It is easy to understand the code snippets.

`AlertMessage` is a `RedirectScoped` bean, which means it is can be access in current request and the next request. It is named with CDI `@Named` which indicates it can be accessed in view via EL by name **flashMessage**.

## MVC Event

MVC defined a series of CDI compatible events, with which you can track the MVC request lifecycle.

MVC provides a `MvcEvent` interface as the base of all events in MVC, there are several specific event implementations.

* AfterControllerEvent
* AfterProcessViewEvent
* BeforeControllerEvent
* BeforeProcessViewEvent
* ControllerRedirectEvent

MVC itself will fire these events in the request processing progress, you can observe the events via CDI `@Observes`.

```java
@ApplicationScoped
public class MvcEventListener {

    @Inject Logger LOGGER;

    private void onControllerMatched(@Observes BeforeControllerEvent event) {
        LOGGER.info(() -> "Controller matched for " + event.getUriInfo().getRequestUri());
    }

    private void onViewEngineSelected(@Observes BeforeProcessViewEvent event) {
        LOGGER.info(() -> "View engine: " + event.getEngine());
    }

    @PostConstruct
    private void init() {
        LOGGER.config(() -> this.getClass().getSimpleName() + " created");
    }
}
```

## Source codes

1. Clone the codes from my GitHub account.

   <https://github.com/hantsy/ee8-sandbox/>
2. Open the **mvc** project in NetBeans IDE.
3. Run it on Glassfish.
4. After it is deployed and running on Glassfish application server, navigate <http://localhost:8080/ee8-mvc/mvc/tasks> in browser.