Talk about the Contexts & Dependency Injection specification introduced in Java EE 6. It's a basic introduction to the most important concepts of the specification. The slide were made for a 50 minute talk at the NL-JUG conference in November 2009.

1. The future of
Enterprise Dependency
Injection
Paul Bakker

2. Outline
• The history of JSR-299
• JSR-299 dependency injection
• Contextual components
• Conversations
• Producers

3. About me
Paul Bakker
• Trainer Info Support Hibernat
EJB 3
e
• NLJUG speaker JSF
Flex
• Java Magazine author Seam
Groovy
JavaFX
Grails
Spring

4. History
WebBeans

5. History
Contexts & Dependency Injection
WebBeans
for the Java EE platform

6. History
Contexts & Dependency Injection
WebBeans
for the Java EE platform
JSR-330 JSR-299
Dependency Uses Contexts & Dependency
Injection for Injection for the Java EE
Java platform
Java SE Java EE

7. JSR-330
• Standardized dependency injection for Java SE
–maximize reusability, testability and
maintainability
• Bob Lee and Rod Johnson
• Specifies annotations and use of annotations
• Does NOT specify a container
• JSR-299 uses JSR-330 annotations

8. JSR-330 annotations
• @Inject
• @Qualifier
• @Named
–String based qualifier
• @Scope
• @Singleton
–singleton scope
• Provider<T>
–provides instances of T

9. JSR-299
• Type safe Dependency Injection for Java EE
components
• Lifecycle aware
–EE components often have a scope/context
–i.e. request scoped JSF managed bean
• Integration with the Unified Expression
Language
• Additional services
–i.e. event notification, decoration and interceptors

10. Implementations
• Reference Implementation:
–WebBeans
• First alternative implementation
–Apache OpenWebBeans
–ASL-Licenced
–aims to provide a new set of WebBeans
components of other Apache projects

11. Implementations
• Reference Implementation:
–WebBeans Weld
• First alternative implementation
–Apache OpenWebBeans
–ASL-Licenced
–aims to provide a new set of WebBeans
components of other Apache projects

12. Exposes bean to EL

13. Bean valid for this request

14. Inject instance of Greeter
An instance will be created
by the container, and bound
to request scope

15. The Greeter class
• The Greeter is a simple POJO

16. The Greeter class
• But could have been a EJB Session Bean...

17. Types of injection
Field injection
Constructor injection
Setter injection

18. Types of injection
Field injection
Constructor injection
Setter injection

19. Where can I use CDI?
• Inject into:
–every POJO
–every EJB Session Bean
–every Servlet
• Injectable types:
–every POJO
–every EJB Session Bean
–JEE Resources (e.g. a DataSource)

20. Stereotypes
• Declare common meta data in a new annotation
–@Model is a standard stereotype

21. Qualifiers
• An interface could have multiple
implementations
–the container must choose an implementation
• Add a qualifier (another annotation) to each
implementation
–the container chooses the correct implementation

22. Qualifiers

23. Qualifiers
Self written qualifier annotation
Self written qualifier annotation

24. Qualifiers

25. Qualifiers
No compile-time
coupling

26. Scopes
• In a web application, an object always has a
scope (e.g. Request or Session scope)
• CDI is context/scope aware
–injection is scope sensitive
–instances may be shared by injection points
–container cleans up
• Scopes: Request, Session, Conversation,
Application
• Default scope: @Dependent
–never shared, bound to lifecycle of injection point

27. Default Scope
@Dependent @Dependent
MyClass MyClass
@Inject @Inject
Request Request
scoped scoped
bean ‘A’ bean ‘B’
request

28. Request Scope
@RequestScoped @RequestScoped
MyClass MyClass
@Inject @Inject @Inject
Request Request Request
scoped scoped scoped
bean ‘A’ bean ‘B’ bean ‘A’
request 1 request 2

29. Session Scope
@SessionScoped
MyClass
@Inject @Inject @Inject
Request Request Request
scoped scoped scoped
bean ‘A’ bean ‘B’ bean ‘A’
request 1 request 2

30. Conversation scope
• Multi-request scope within a session
• Isolated from other conversations
• Defined begin and end point
browser tab 2
find room book room step 2 confirm
browser tab 1
find room book room step 2 confirm
Login Logout

31. Conversations example
Conversational bean
Upgrade to
long-running
Schedule end of
conversation at
end of request

32. Producer methods
• A source of injectable objects
–objects are not required to be beans (e.g. a List)
–concrete type varies at runtime
–objects require extra initialization
• Most similar to a traditional Factory Method
–but more loosely coupled

33. Producer methods

34. Producer methods

35. Producer methods
Exposed to EL

36. Producer methods
Put in Application Scope

37. Producer methods
Custom qualifier

38. Using CDI
• CDI is part of JEE 6
–Every JEE 6 app server must be CDI compatible
–GlassFish V3 and JBoss 5.2 bundled with Weld
• Weld can be installed on Tomcat or Jetty

39. The verdict
Pros
• Finally a decent DI
framework
• Makes extreme loose
coupling possible
Cons
• Can code be too
decoupled?
• Where did my instance
come from?

40. More about this
• January 11: Season Class
• Bert Ertman & Paul Bakker

41. More about this
• January 11: Season Class
–JSF 2.0
–Servlet 3.0
–EJB 3.1 (lite)
–JPA 2.0
–Contexts & DI
–JAX-RS
–JavaFX