从JBoss Seam 2.x迁移到JavaEE 7之二：组件的有效范围Scope

JBoss Seam 2.x提供了预置的几种Scope，如@Scope(ScopeType.SESSION)等，但不能扩展。

JavaEE 7 CDI也提供了预置的几种Scope，如@SessionScoped。此外，还可以扩展实现新的Scope。

两者内置的Scope的对比：

Seam 2 Scope	CDI Scope
Event	@RequestScoped
Session	@SessionScoped
Stateless	No exact match.  The stateless scope is used primarily for Stateless Session Beans (EJB) in Seam 2. A Stateless session bean can be bound to the @Dependent context in a CDI application.
No exact match	@Dependent Means creating a new instance for each injection point.
Page	No exact match.
Conversation	No exact match.  There are several alternatives which help to maintain conversational state: CDI @ConversationScoped — keeps conversational state between many requests, needs to be programmatically started and stopped. JSF Flash scope — keeps state between two requests and possibly different views. DeltaSpike Grouped Conversation scope — keeps state per-window, is started automatically when a grouped-conversation-scoped bean is accessed, maintains separate conversations for each bean or groups of beans.