DEPENDENCY INJECTION AND CDI - Java EE Design Patterns - page 57

empty. The CDI scans the classes in the archive looking for any class that conforms to the bean
requirements detailed earlier and manages and injects any such class that is not annotated with
@Vetoed . This annotation excludes that class from being managed by the container.
In some cases, it may not be desirable to allow the container to manage any conformant bean it
i nds. If you want to restrict what the CDI container considers to be a managed bean, you can dei ne
the bean‐discovery‐mode property in the bean.xml deployment descriptor. Listing 5‐10 shows a
snippet of the bean.xml i le that dei nes the bean‐discovery‐mode property as ALL .

LISTING 5‐10: The bean discovery mode is set in the bean.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns=" http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi=" http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation=" http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd"
version="1.1" bean‐discovery‐mode="all">
...
</beans>

The bean‐discovery‐mode property can take one of three values: ALL . The

ALL property instructs the CDI container to manage all beans that it i nds in the archive. This is the
default. The NONE property means that the CDI container will manage no beans, and the ANNOTATED
property makes the archive behave like an implicit archive. In this case, the container scans for
beans with annotated scope types.

, NONE , or ANNOTATED

An implicit bean archive does not contain a bean.xml deployment descriptor. This signals to the
CDI container that the container should only manage beans with a scope. Further details about
scoped beans are discussed later in the section, “Contexts and Scope.”

The @Inject Annotation
The @Inject annotation and its capabilities have already been covered. Before CDI in Java EE was
introduced, each DI framework offered its own way of injecting resources. When the Java EE CDI
container was released to work alongside the EJB container, @Inject annotation became a unique
and abstract interface for almost all inject operations. The @Inject annotation lets you use any
appropriate container or DI framework referenced for the case.

Contexts and Scope
Context is the difference between EJBs and CDI containers. Each CDI bean's life cycle is bound to a
context scope. The CDI offers four different scopes:
➤

@RequestScoped —Duration is a user's HTTP request.

➤

@SessionScoped —Duration is a user's HTTP session.

➤

@ApplicationScoped —State is shared across all users for the duration of the application.

➤

@ConversationScoped —Scope duration is controlled by the developer.