5.2. Seam components

Seam components are Plain Old Java Objects (POJOs). Specifically, they are JavaBeans, or Enterprise JavaBean 3.0 (EJB3) enterprise beans. While Seam does not require components to be EJBs, and can be used without an EJB3-compliant container, Seam was designed with EJB3 in mind, and includes deep integration with EJB3. Seam supports the following component types:
  • EJB3 stateless session beans
  • EJB3 stateful session beans
  • EJB3 entity beans (for instance, JPA entity classes)
  • JavaBeans
  • EJB3 message-driven beans
  • Spring beans (see Chapter 26, Spring Framework integration)

5.2.1. Stateless session beans

Stateless session bean components cannot hold state across multiple invocations, so they usually operate upon the state of other components in the various Seam contexts. They can be used as JSF action listeners, but cannot provide properties to JSF components for display.
Stateless session beans always exist in the stateless context. They can be accessed concurrently as a new instance is used for each request. The EJB3 container assigns instances to requests. (Normally, instances are allocated from a reuseable pool, so instance variables can retain data from previous uses of the bean.)
Seam stateless session bean components are instantiated with either Component.getInstance() or @In(create=true). They should not be directly instantiated via JNDI look up or the new operator.