JSR-299 defines a unifying dependency injection and contextual lifecycle model for Java EE 6. It includes producer methods that allow control over object creation, and events that decouple event producers and observers. The reference implementation Weld is featured complete and integrated into application servers like JBoss and GlassFish. Feedback is being used to finalize the specification.

1. J SR-2 9 9
Co n t e x t & De p e n d e n c y
Injec t ion
Max Rydahl Andersen
JBossian, Red Hat
27th. November
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2. Ro a d M a p
Background
Concepts
Status
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3. J av a EE 6
• The EE 6 web profile removes most of the “cruft” that
has developed over the years
• mainly totally useless stuff like web services, EJB 2 entity
beans etc.
• some useful stuff (e.g. JMS) is missing, but vendors can
include it
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4. J av a EE 6
• EJB 3.1 - asynch, no-interface views, embeddable
• JPA 2.0 - typesafe criteria API, many more O/R mapping
options
• JSF 2.0 - Ajax, easy component creation, bookmarkable
URLs
• Bean Validation 1.0 - annotation-based validation API
• Servlet 3.0 - async support, better support for
frameworks
• Standard global JNDI names
• Managed Beans
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5. Managed Beans
• Container-managed POJOs with minimal requirements
• support a set of basic services
• resource injection
• lifecycle callbacks
• interceptors
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6. Managed Beans
• the foundation for all other component types in the
platform
• core services centralized under Managed Beans
• Other specifications will add support for additional
services
• remoting
• instance pooling
• web services
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7. Go a l s
• JSR-299 defines a unifying dependency injection and
contextual lifecycle model for Java EE 6
• a completely new, richer dependency management
model
• designed for use with stateful objects
• integrates the “web” and “transactional” tiers
• makes it much easier to build applications using JSF and
EJB together
• includes a complete SPI allowing third-party frameworks
to integrate cleanly in the EE 6 environment
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8. Loose c oupling
• Events, interceptors and decorators enhance the loose-
coupling that is inherent in this model:
• event notifications decouple event producers from event
consumers
• interceptors decouple technical concerns from business
logic
• decorators allow business concerns to be
compartmentalized
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9. Go i n g b e yo n d t h e s p e c
• Weld provides extra integrations
• Tomcat/Jetty/Google App Engine support
• Java SE support
• OSGi containers
• ???
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10. Go i n g b e yo n d t h e s p e c
• and features which can be used in any CDI
environment
• Seam2 bridge
• Spring bridge
• Wicket support
• Logger
• Prototype new ideas for the next version of the spec
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11. Se a m 3
• Use the CDI core
• Provide a development environment
• JBoss Tools
• Seam-gen (command line tool)
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12. Se a m 3
• include a set of modules for any container which
includes CDI
• jBPM integration
• Seam Security
• Reporting (Excel/PDF)
• Mail
• etc.
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13. Ro a d M a p
Background
Concepts
Status
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14. Es s e n t i a l i n g r e d i e n t s
• API types
• Qualifier annotations
• Scope
• Alternatives
• A name (optional)
• Interceptors and Decorators
• The implementation
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15. Si m p l e Ex a m p l e
public class Hello { Any Managed Bean
public String sayHello(String name) {
return "hello" + name; can use these
} services
}
@Stateless So can EJBs
public class Hello {
public String sayHello(String name) {
return "hello" + name;
}
}
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16. Si m p l e Ex a m p l e
public class Printer { @Inject defines an
injection point. @Default
@Inject Hello hello; qualifier is assumed
public void printHello() {
System.out.println( hello.sayHello("world") );
}
}
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17. Co n s t r u c t o r i n j e c t i o n
Mark the constructor to be
public class Printer { called by the container
private Hello hello; @Inject
@Inject
public Printer(Hello hello) { this.hello=hello; }
public void printHello() {
System.out.println( hello.sayHello("world") );
}
}
Constructors are injected by
default; @Default is the
default qualifier
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18. We b B e a n N a m e s
@Named("hello")
public class Hello {
By default not
public String sayHello(String name) { available through EL.
return "hello" + name;
}
} If no name is specified, then
a default name is used. Both
these Managed Beans have
@Named the same name
public class Hello {
public String sayHello(String name) {
return "hello" + name;
}
}
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19. J SF Pa g e
<h:commandButton value=“Say Hello”
action=“#{hello.sayHello}”/>
Calling an action on a
bean through EL
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20. Qu a l i f i e r
A qualifier is an annotation that lets a client choose
between multiple implementations of an API at runtime
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21. De f i n e a q u a l i f i e r
@Retention(RUNTIME)
@Target({TYPE, METHOD, FIELD, PARAMETER})
@Qualifier
public @interface Casual {} Creating a qualifer
is really easy!
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22. Using a qualifier
@Casual
We also specify the
public class Hi extends Hello {
public String sayHello(String name) {
@Casual qualifier. If
return "hi" + name; no qualifer is specified
} on a bean, @Default
} is assumed
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23. Using a qualifier
Here we inject the Hello
bean, and require an
public class Printer { implementation which is
@Inject @Casual Hello hello; qualified by @Casual
public void printHello() {
System.out.println( hello.sayHello("JBoss") );
}
}
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24. A l t e r n at i ve s
• An alternative bean is one which must be specifically
enabled for a particular deployment
• It replaces the managed or session bean for which it is
an alternative
• May also completely replace it
• all producers and observers defined on original bean are
disabled for this deployment)
• Alternatives enabled in XML deployment descriptor
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25. De f i n i n g a n a l t e r n at i ve
@Alternative Same API, different
public class Hola extends Hello { implementation
public String sayHello(String name) {
return "hola " + name;
}
}
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26. En a b l i n g a n a l t e r n at i ve
<beans>
<alternatives>
<class>com.acme.Hola</class>
<sterotype>com.acme.SouthernEuropean</stereotype>
</alternatives>
</beans>
Can also define a sterotype as
an alternatives. Any
stereotyped beans will be an
alternative
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27. St e r e o t y p e s
• We have common architectural “patterns” in our
application, with recurring roles
• Capture the roles using stereotypes
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28. St e r e o t y p e s
• A stereotype encapsulates any combination of:
• a default scope, and
• a set of interceptor bindings.
• A stereotype may also specify that:
• all beans with the stereotype have defaulted bean EL
names
• all beans with the stereotype are alternatives
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29. Cr e at i n g a s t e r e o t y p e
@RequestScoped Scope
@Named
@Alternative
@Stereotype Has a defaulted name
@Retention(RUNTIME)
@Target(TYPE)
public @interface AlternativeAction{}
All stereotyped beans
become alternatives
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30. Using a st ereot ype
@AlternativeAction
public class Hello {
public String sayHello(String name) {
return "hi " + name;
}
}
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31. Sc o p e s a n d Co n t ex t s
• Built-in scopes:
• Any servlet - @ApplicationScoped,
@RequestScoped, @SessionScoped
• JSF requests - @ConversationScoped
• Dependent scope (De fa u l t ): @Dependent
• Custom scopes
• A scope type is an annotation, can write your own
context implementation and scope type annotation
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32. Sc o p e s
@SessionScoped
public class Login { Session scoped
private User user;
public void login() {
user = ...;
}
public User getUser() { return user; }
}
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33. Sc o p e s
public class Printer {
No coupling between
@Inject Hello hello; scope and use of
@Inject Login login; implementation
public void printHello() {
System.out.println(
hello.sayHello( login.getUser().getName() ) );
}
}
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34. Pr o d u c e r m e t h o d s
• Producer methods allow control over the production of a
bean where:
• the objects to be injected are not managed instances
• the concrete type of the objects to be injected may vary
at runtime
• the objects require some custom initialization that is not
performed by the bean constructor
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35. Pr o d u c e r m e t h o d s
@SessionScoped
public class Login {
private User user;
public void login() {
user = ...;
}
@Produces
User getUser() { return user; }
}
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36. Pr o d u c e r m e t h o d s
public class Printer {
@Inject Hello hello;
@Inject User user; Much better, no
public void hello() { dependency on
System.out.println( Login!
hello.sayHello( user.getName() ) );
}
}
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37. Pr o d u c e r Fi e l d s
• Simpler alternative to Producer methods
Similar to
@SessionScoped outjection in
public class Login {
Seam
@Produces @LoggedIn @RequestScoped
private User user;
public void login() {
user = ...;
}
}
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38. J av a EE Re s o u r c e s
public class PricesTopic {
@Produces @Prices
@Resource(name="java:global/env/jms/Prices")
Topic pricesTopic;
}
public class UserDatabasePersistenceContext {
@Produces @UserDatabase
@PersistenceContext
EntityManager userDatabase;
}
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39. Eve n t s
• Event producers raise events that are then delivered to
event observers by the Web Bean manager.
• not only are event producers decoupled from observers;
observers are completely decoupled from producers
• observers can specify a combination of "selectors" to
narrow the set of event notifications they will receive
• observers can be notified immediately, or can specify that
delivery of the event should be delayed until the end of
the current transaction
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40. Ev e n t s Inject an instance of Event. Additional
qualifiers can be specified to narrow the
event consumers called. API type
specified as a parameter on Event
public class Hello {
@Inject @Any Event<Greeting> greeting;
public void sayHello(String name) {
greeting.fire( new Greeting("hello " + name) );
}
}
“Fire” an event, the
producer will be notified
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41. Ev e n t s
Observer methods, take the API
public class Printer { type and additional qualifiers
void onGreeting(@Observes Greeting greeting,
@Default User user) {
System.out.println(user + “ says “ + greeting);
}
}
Additional parameters can
be specified and will be
injected by the container
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42. Ro a d M a p
Background
Concepts
Status
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43. J SR-2 9 9 : Co n t ex t s a n d De p e n d e n c y
I n j e c t i o n fo r J av a EE
• Proposed Final Draft 2 published
• Reference Manual being written now
• http://www.seamframework.org/Weld
• look for an update soon!
• Send feedback to jsr-299-comments@jcp.org
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44. We l d
• The Reference implementation
• Feature complete preview of PFD2. Download it, try it
out, give feedback!
• http://seamframework.org/Download
• Working on second release candidate
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45. We l d
• Integrated into:
• JBoss 5.1.0.GA and above (6.0.0.Beta1 coming soon)
• GlassFish V3 (get a recent build)
• Available as an addon for:
• Tomcat 6.0.x
• Jetty 6.1.x
• Java SE
• Google App Engine
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46. J B o s s CDI To o l s (Wo r k i n p r o g r e s s )
• Code completion for @Named components
• Validation of CDI constructs (”red squigly lines”)
• Ambigious injection points
• Non-matching injection
•…
• CDI component explorer
• Show possible injection points for a given line
• Show matching event types
• Refactoring of EL result in updates to @Named
• ...
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47. Q& A
http://in.relation.to/Bloggers/Max
http://www.seamframework.org/Weld
http://jcp.org/en/jsr/detail?id=299
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