Components

Model differences

Seam 2 uses as a basic building block a Component. While Java EE 6 and CDI defines a Managed Bean as basic building block.

While both Seam 2 and CDI supports definition of metadata with help of annotations, Seam 2 XML configuration was left uncovered in CDI specification.

Table 1. Differences in component model

Seam 2	CDI	Note
Session Bean	Session Bean
Java Bean	Managed Bean
Factory method	Producer method/field	A producer can inject parameters into a method while Seam 2 Factory method can not
Message-driven Bean	Message-driven Bean	In Seam 2 MDB may not be bound to a Seam context
Entity Bean	Entity Bean	In Seam 2 Entity beans do not support bijection or context demarcation
	Resource	Reference to a Java EE resource
Component	Portable Extension	It may provide other kinds of beans

Additionally there are some differences how a Managed Bean is defined in comparison to Seam 2 Component. Look in the following table.

Table 2. Component metadata differences

Seam 2 component	CDI Managed Bean	Note
must have @Name	no need to have it	do not have to have @Named
available in EL	only if @Named is defined
Bijection	no bijection
seam.properties or components.xml	beans.xml
explicit definition	implicit recognition	every Java class in the bean archive that meets certain conditions is implicitly recognized as a managed bean — no special declaration is required, while Seam 2 needs @Name or inclusion in XML descriptor

Table 3. Component/Managed Bean metadata

Seam 2	CDI
name → @Name	name (optional) @Named
scope → @Scope	scope → every scope has special annotation
roles → @Roles – single Java class to act as a base for multiple components (comprises name and a scope)	Bean type and @Qualifier  — used to distinguish between multiple components sharing the same bean type
conditional installation → @Install	conditional installation → @Alternative,@Specializes,@Veto,@Requires

Asynchronicity

Seam 2 supports asynchronous method invocation via Dispatcher available components. Several implementations are available, like TimerService or Quartz Scheduler.

In contrast CDI does not specify asynchronous method invocation and you need to rely on EJB @Asynchronous observer methods.

Seam Bijection

Bijection is performed dynamically via an Interceptor for every component method invocation. Bijection is bidirectional injection and outjection.

CDI doesn’t support bijection and does a static injection, which is performed only once per component lifecycle:

• when creating contextual objects

• injection points: constructor, field, initializer method

• typesafe resolution — the process of matching a bean to an injection point

• bean is assignable to a given injection point if it has a bean type that matches the required type has all the required qualifiers

• ambiguous and unsatisfied dependency is an error

• no outjection and disinjection

• beans are initialized automatically