Overview (CDI APIs 1.2 API)

Packages
Package	Description
javax.decorator	Annotations relating to decorators.
javax.enterprise.context	Annotations and interfaces relating to scopes and contexts.
javax.enterprise.context.spi	The custom context SPI.
javax.enterprise.event	Annotations and interfaces relating to events.
javax.enterprise.inject	Annotations relating to bean and stereotype definition, built-in qualifiers, and interfaces and classes relating to programmatic lookup.
javax.enterprise.inject.spi	The portable extension integration SPI.
javax.enterprise.util	Contains shared, general-purpose helper classes and annotations.

Contexts and Dependency Injection (CDI) defines a set of complementary services that help improve the structure of application code.

A well-defined lifecycle for stateful beans bound to well-defined lifecycle contexts, where the set of contexts is extensible
A sophisticated, typesafe dependency injection mechanism, including the ability to select dependencies at either development or deployment time, without verbose configuration
Support for Java EE modularity and the Java EE component architecture—the modular structure of a Java EE application is taken into account when resolving dependencies between Java EE components
Integration with the Unified Expression Language, allowing any bean to be used directly within a JSF or JSP page
The ability to decorate injected beans
The ability to associate interceptors with beans via typesafe interceptor bindings
An event notification model
A web conversation context in addition to the three standard web contexts defined by the Java Servlets specification
An SPI allowing portable extensions to integrate cleanly with the container

CDI allows objects to be bound to lifecycle contexts, to be injected, to be associated with interceptors and decorators, and to interact in a loosely coupled fashion by firing and observing events. Various kinds of objects are injectable, including EJB 3 session beans, managed beans, producer methods and Java EE resources. We refer to these objects in general terms as beans and to instances of beans that are bound to contexts as contextual instances.