Java EE 7 Essentials

Chapter 9. Contexts and Dependency Injection

Contexts and Dependency Injection (CDI) is defined as JSR 346, and the complete specification can be downloaded.

CDI defines a type-safe dependency injection mechanism in the Java EE platform. A bean specifies only the type and semantics of other beans it depends upon, without a string name and using the type information available in the Java object model. This allows compile-time validation in addition to deployment. It also provides for easy refactoring.

The injection request need not be aware of the actual life cycle, concrete implementation, threading model, or other clients of the bean. This “strong typing, loose coupling” combination makes your code easier to maintain. The bean so injected has a well-defined life cycle and is bound to life-cycle contexts. The injected bean is also called a contextual instance because it is always injected in a context.

Almost any POJO can be injected as a CDI bean. This includes EJBs, JNDI resources, entity classes, and persistence units and contexts. Even the objects that were earlier created by a factory method can now be easily injected. Specifically, CDI allows EJB components to be used as JSF managed beans, thus bridging the gap between the transactional and the web tier. It is also integrated with Unified Expression Language (UEL), allowing any contextual object to be used directly within a JSF or JSP page.

Discovery of Beans

Bean classes are deployed in bean archives. A bean archive has the bean ...