1.
CDI (JSR-299), Weld and
the future of Seam
Dan Allen
Senior Software Engineer
JBoss by Red Hat

2.
Who am I?
● Author of Seam in Action, Manning 2008
● Seam Community Liaison
● Weld, Seam & Arquillian project member
● JSR-314 (JSF 2) EG representative
● Open Source advocate
mojavelinux
2 CDI (JSR-299), Weld and the future of Seam | Dan Allen

3.
Agenda
● Terminology
● Why JSR-299?
● JSR-299 themes
● Brief tour of programming model
● Weld
● Seam
3 CDI (JSR-299), Weld and the future of Seam | Dan Allen

4.
Technology terminology
● CDI (JSR-299)
● Contexts & dependency injection for Java EE
● Weld
● JSR-299 Reference Implementation & TCK
● Extended CDI support (Servlets, Java SE)
● CDI enhancements for extension writers
● Maven archetypes for CDI and Java EE
● Seam 3
● Portable extensions for Java EE
● Integrations with non-Java EE technologies
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5.
Stated goal of JSR-299
Web tier Transactional tier
(JSF) (EJB)
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6.
Why reinvest?
Java EE 5
6
Seam 2 CDI (JSR-299), Weld and the future of Seam | Dan Allen

7.
What CDI provides
● Services for Java EE components
● Lifecycle management of stateful beans bound to
well-defined contexts (including conversation context)
● A type-safe approach to dependency injection
● Interaction via an event notification facility
● Reduced coupling between interceptors and beans
● Decorators, which intercept specific bean instances
● Unified EL integration (bean names)
● SPI for developing extensions for the Java EE platform
● Java EE architecture  flexible, portable, extensible
7 CDI (JSR-299), Weld and the future of Seam | Dan Allen

8.
What CDI provides
● Services for Java EE components
● Lifecycle management of stateful beans bound to
well-defined contexts (including conversation context)
● A type-safe approach to dependency injection
● Interaction via an event notification facility
● Reduced coupling between interceptors and beans
● Decorators, which intercept specific bean instances
● Unified EL integration (bean names)
● SPI for developing extensions for the Java EE platform
● Java EE architecture  flexible, portable, extensible
8 CDI (JSR-299), Weld and the future of Seam | Dan Allen

9.
CDI: The big picture
● Fill in
● Catalyze
● Evolve
9 CDI (JSR-299), Weld and the future of Seam | Dan Allen

10.
Why injection?
● Weakest aspect of Java EE 5
● Fixed set of injectable resources
● @EJB
● @PersistenceContext, @PersistenceUnit
● @Resource (e.g., DataSource, UserTransaction)
● Name-based injection is fragile
● Not “refactor friendly”
● Requires special tooling to validate
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11.
JSR-299 theme
@Produces @WishList
Loose coupling... List<Product> getWishList()
Event<Order>
@InterceptorBinding
@Inject @UserDatabase EntityManager
@Observes
@Qualifier ...with strong typing
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12.
Loose coupling
●
Decouple server and client
● Using well-defined types and “qualifiers”
● Allows server implementation to vary
●
Decouple lifecycle of collaborating components
● Automatic contextual lifecycle management
● Stateful components interact like services
●
Decouple orthogonal concerns (AOP)
● Interceptors & decorators
●
Decouple message producer from consumer
● Events
12 CDI (JSR-299), Weld and the future of Seam | Dan Allen

13.
Strong typing
● Type-based injection
● Eliminate reliance on string-based names
● Compiler can detect typing errors
● No special authoring tools required
● Casting mostly eliminated
● Semantic code errors detected at application startup
● Tooling can detect ambiguous dependencies
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14.
Leverage and extend Java’s type system
@Annotation <TypeParam>
This information is pretty useful!
Type
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15.
Who's bean is it anyway?
● Everyone throwing around this term “bean”
● JSF
● EJB
● Seam
● Spring
● Guice
● CDI
● Need a “unified bean definition”
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16.
Managed bean specification
● Common bean definition
● Instances are managed Managed
by the container Beans
● Common services
● Interceptors
● Resource injections
● Lifecycle callbacks JSF EJB CDI JAX-RS
● Foundation spec
How managed beans evolved: http://www.infoq.com/news/2009/11/weld10
16 CDI (JSR-299), Weld and the future of Seam | Dan Allen

17.
CDI bean ingredients
● Auto-discovered
● Set of bean types
● Set of qualifiers
● Scope
● Bean EL name (optional)
● Set of interceptor bindings
● Alternative classification
● Bean implementation class
17 CDI (JSR-299), Weld and the future of Seam | Dan Allen

18.
Welcome to CDI, managed beans!
public class Welcome {
public String buildPhrase(String city) {
return "Welcome to " + city + "!";
}
}
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19.
Welcome to CDI, EJB 3.1 session beans!
@Stateless public class Welcome {
public String buildPhrase(String city) {
return "Welcome to " + city + "!";
}
}
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20.
When is a bean recognized?
● Bean archive (WAR) ● Bean archive (JAR)
beans.xml can be empty!
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21.
Injection 101
public class Greeter {
@Inject Welcome w;
public void welcome() { @Default qualifier implied
@Default qualifier implied
System.out.println(
w.buildPhrase("Reston"));
}
}
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22.
Where can it be injected?
● Field
● Method parameter
● Constructor*
● Initializer
● Producer
● Observer
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23.
What can be injected?
Managed bean
Object returned by producer
EJB session bean (local or remote)
Java EE resource (DataSource, JMS destination, etc)
JTA UserTransaction
Persistence unit or context
Security principle
Bean Validation factory
Web service reference
Additional resources introduced through SPI
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24.
The bean vs “the other implementation”
● Multiple implementations of same interface
● One implementation extends another
public class Welcome {
public String buildPhrase(String city) {
return "Welcome to " + city + "!";
}
}
public class TranslatingWelcome extends Welcome {
@Inject GoogleTranslator translator;
public String buildPhrase(String city) {
return translator.translate(
"Welcome to " + city + "!");
}
}
24 CDI (JSR-299), Weld and the future of Seam | Dan Allen

25.
Quiz: Now which implementation gets injected?
public class Greeter {
private Welcome welcome;
@Inject
void init(Welcome welcome) {
this.welcome = welcome;
}
...
}
It's ambiguous!
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26.
Settling an ambiguous resolution
● Qualifier
● Alternative
● Hide bean types
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27.
qualifier
n. an annotation used to resolve an API
implementation variant at an injection point
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28.
Defining a qualifier
● A qualifier is an annotation
@Qualifier
@Retention(RUNTIME)
@Target({TYPE, METHOD, FIELD, PARAMETER})
public @interface Translating {}
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29.
Qualifying an implementation
● Adding a qualifier annotation:
● makes type more specific
● assigns semantic meaning
@Translating
public class TranslatingWelcome extends Welcome {
@Inject GoogleTranslator translator;
public String buildPhrase(String city) {
return translator.translate(
"Welcome to " + city + "!");
}
}
29 CDI (JSR-299), Weld and the future of Seam | Dan Allen

30.
Qualifier as a “binding type”
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31.
Using a specific implementation
● Qualified implementation must be requested explicitly
● Akin to the factory method pattern
● Resolves ambiguity at injection point!
public class Greeter {
private Welcome welcome; No reference to implementation class!
No reference to implementation class!
@Inject
void init(@Translating Welcome welcome) {
this.welcome = welcome
}
public void welcomeVisitors() {
System.out.println(
welcome.buildPhrase("Reston"));
}
}
31 CDI (JSR-299), Weld and the future of Seam | Dan Allen

32.
Alternative bean
● Swap replacement implementation per deployment
● Replaces bean and its producer methods and fields
● Disabled by default
● Must be activated in /META-INF/beans.xml
Put simply: an override
32 CDI (JSR-299), Weld and the future of Seam | Dan Allen

33.
Defining an alternative
@Alternative
public class TranslatingWelcome extends Welcome {
@Inject GoogleTranslator translator;
public String buildPhrase(String city) {
return translator.translate(
"Welcome to " + city + "!");
}
}
33 CDI (JSR-299), Weld and the future of Seam | Dan Allen

34.
Substituting the alternative
● Implementation must be activated using beans.xml
<beans>
<alternatives>
<class>com.acme.TranslatingWelcome</class>
</alternatives>
</beans>
34 CDI (JSR-299), Weld and the future of Seam | Dan Allen

35.
Assigning a bean name
@Named("greeter")
public class Greeter {
private Welcome welcome;
@Inject
void init(Welcome welcome) {
this.welcome = welcome;
}
public void welcomeVisitors() {
System.out.println(
welcome.buildPhrase("Reston"));
}
}
35 CDI (JSR-299), Weld and the future of Seam | Dan Allen

36.
Assigning a bean name by convention
@Named
public class Greeter {
private Welcome welcome; Bean name is decapitalized
Bean name is decapitalized
simple class name
simple class name
@Inject
void init(Welcome welcome) {
this.welcome = welcome;
}
public void welcomeVisitors() {
System.out.println(
welcome.buildPhrase("Reston"));
}
}
36 CDI (JSR-299), Weld and the future of Seam | Dan Allen

37.
Welcome to CDI, JSF!
● Use the bean directly in the JSF view
<h:form>
<h:commandButton value="Welcome visitors"
action="#{greeter.welcomeVisitors}"/>
</h:form>
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38.
JSF
managed JSP
beans
CDI Facelets
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39.
Stashing the bean in a context
● Bean saved for the duration of a request
@RequestScoped
@Named("greeter")
public class Greeter {
private Welcome welcome;
private String city; // getter and setter hidden
@Inject
void init(Welcome welcome) {
this.welcome = welcome
}
public void welcomeVisitors() {
System.out.println(welcome.buildPhrase(city));
}
}
39 CDI (JSR-299), Weld and the future of Seam | Dan Allen

40.
Collapsing layers with state management
● Now it’s possible for bean to hold state
<h:form>
<h:inputText value="#{greeter.city}"/>
<h:commandButton value="Welcome visitors"
action="#{greeter.welcomeVisitors}"/>
</h:form>
● Satisfies initial goal of JSR-299
● ...in fact, integrates JSF and any managed bean
40 CDI (JSR-299), Weld and the future of Seam | Dan Allen

41.
Scope types and contexts
● Absence of scope - @Dependent
● Bound to lifecycle of bean holding reference
● Servlet scopes
● @ApplicationScoped
● @RequestScoped
● @SessionScoped
● JSF conversation scope - @ConversationScoped
● Custom scopes
● Define scope type annotation (e.g., @FlashScoped)
● Implement the context API in an extension
41 CDI (JSR-299), Weld and the future of Seam | Dan Allen

42.
Scope transparency
● Scopes not visible to client
● No coupling between scope and use of type
● Scoped beans are proxied for thread safety
42 CDI (JSR-299), Weld and the future of Seam | Dan Allen

43.
Conversation context
● Request <= Conversation << Session
●
● Boundaries demarcated by application
● Optimistic transaction
● Conversation-scoped persistence context
● No fear of exceptions on lazy fetch operations
43 CDI (JSR-299), Weld and the future of Seam | Dan Allen

44.
Controlling the conversation
@ConversationScoped
public class BookingAgent {
@Inject @BookingDatabase EntityManager em;
@Inject Conversation conversation;
private Hotel selected;
private Booking booking;
public void select(Hotel h) {
selected = em.find(Hotel.class, h.getId());
conversation.begin();
}
...
44 CDI (JSR-299), Weld and the future of Seam | Dan Allen

45.
Controlling the conversation
...
public boolean confirm() {
if (!isValid()) {
return false;
}
em.persist(booking);
conversation.end();
return true;
}
}
45 CDI (JSR-299), Weld and the future of Seam | Dan Allen

46.
producer method
n. a method whose return value produces
an injectable object
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47.
Producer method examples
@Produces @RequestScoped
public FacesContext getFacesContext() { From non-bean
From non-bean
return FacesContext.getInstance();
}
@Produces
public PaymentProcessor getPaymentProcessor(
@Synchronous PaymentProcessor sync,
Runtime selection
Runtime selection
@Asynchronous PaymentProcessor async) {
return isSynchronous() ? sync : async;
}
@Produces @SessionScoped @WishList Custom setup
Custom setup
public List<Product> getWishList() {
return em.createQuery("...").getResultList();
}
47 CDI (JSR-299), Weld and the future of Seam | Dan Allen

48.
Bridging Java EE resources
● Use producer field to expose Java EE resource
@Stateless
public class UserEntityManagerProducer {
@Produces @UserRepository
@PersistenceContext(unitName = "userPU")
EntityManager em;
}
@Stateless
public class PricesTopicProducer {
@Produces @Prices
@Resource(name = "java:global/env/jms/Prices")
Topic pricesTopic;
}
48 CDI (JSR-299), Weld and the future of Seam | Dan Allen

49.
Injecting resource in type-safe way
● String-based resource names are hidden
public class UserManager {
@Inject @UserRepository EntityManager userEm;
...
}
public class StockDisplay {
@Inject @Prices Topic pricesTopic;
...
}
49 CDI (JSR-299), Weld and the future of Seam | Dan Allen

50.
Rethinking interceptors
@Interceptors(
SecurityInterceptor.class,
TransactionInterceptor.class,
LoggingInterceptor.class
)
@Stateful public class BusinessComponent {
...
}
Um, what's the point?
50 CDI (JSR-299), Weld and the future of Seam | Dan Allen

51.
Interceptor wiring in JSR-299 (1)
● Define an interceptor binding type
@InterceptorBinding
@Retention(RUNTIME)
@Target({TYPE, METHOD})
public @interface Secure {}
51 CDI (JSR-299), Weld and the future of Seam | Dan Allen

52.
Interceptor wiring in JSR-299 (2)
● Marking the interceptor implementation
@Secure
@Interceptor
public class SecurityInterceptor {
@AroundInvoke
public Object aroundInvoke(InvocationContext ctx)
throws Exception {
// ...enforce security...
ctx.proceed();
}
}
52 CDI (JSR-299), Weld and the future of Seam | Dan Allen

53.
Interceptor wiring in JSR-299 (3)
● Applying interceptor with proper semantics
@Secure
public class AccountManager {
public boolean transfer(Account a, Account b) {
...
}
}
53 CDI (JSR-299), Weld and the future of Seam | Dan Allen

54.
Multiple interceptors
● Application developer only concerned about semantics
@Transactional
public class AccountManager {
@Secure
public boolean transfer(Account a, Account b) {
...
}
}
54 CDI (JSR-299), Weld and the future of Seam | Dan Allen

55.
Enabling and ordering interceptors
● Bean archive has no enabled interceptors by default
● Interceptors activated in beans.xml of bean archive
● Referenced by binding type
● Ordering is per-module
● Declared in module in which the interceptor is used
<beans>
<interceptors>
<class>com.acme.SecurityInterceptor</class>
<class>com.acme.TransactionInterceptor</class>
</interceptors>
</beans>
Interceptors applied in order listed
Interceptors applied in order listed
55 CDI (JSR-299), Weld and the future of Seam | Dan Allen

56.
Composite interceptor bindings
● Interceptor binding types can be meta-annotations
public
@Secure
@Transactional
@InterceptorBinding Order does not matter
Order does not matter
@Retention(RUNTIME)
@Target(TYPE)
@interface BusinessOperation {}
56 CDI (JSR-299), Weld and the future of Seam | Dan Allen

57.
Multiple interceptors (but you won’t know it)
● Interceptors inherited from composite binding types
public
@BusinessOperation
class AccountManager {
public boolean transfer(Account a, Account b) {
...
}
}
57 CDI (JSR-299), Weld and the future of Seam | Dan Allen

58.
Wrap up annotations using stereotypes
● Common architectural patterns – recurring roles
● A stereotype packages:
● A default scope
● A set of interceptor bindings
● The ability to that beans are named
● The ability to specify that beans are alternatives
58 CDI (JSR-299), Weld and the future of Seam | Dan Allen

59.
Annotation jam!
● Without stereotypes, annotations pile up
public
@Secure
@Transactional
@RequestScoped
@Named
class AccountManager {
public boolean transfer(Account a, Account b) {
...
}
}
59 CDI (JSR-299), Weld and the future of Seam | Dan Allen

60.
Defining a stereotype
● Stereotypes are annotations that group annotations
public
@Secure
@Transactional
@RequestScoped
@Named
@Stereotype
@Retention(RUNTIME)
@Target(TYPE)
@interface BusinessComponent {}
60 CDI (JSR-299), Weld and the future of Seam | Dan Allen

61.
Using a stereotype
● Stereotypes give a clear picture, keep things simple
public
@BusinessComponent
class AccountManager {
public boolean transfer(Account a, Account b) {
...
}
}
61 CDI (JSR-299), Weld and the future of Seam | Dan Allen

62.
Events
● Completely decouple action and reactions
● Selectors tune which event notifications are received
● Can be observed:
● immediately,
● after transaction completion or
● asynchronously (via extension)
62 CDI (JSR-299), Weld and the future of Seam | Dan Allen

63.
Firing an event Event instance with
Event instance with
type-safe payload
type-safe payload
public class GroundController {
@Inject @Landing Event<Flight> flightLanding;
public void clearForLanding(String flightNum) {
flightLanding.fire(new Flight(flightNum));
}
}
63 CDI (JSR-299), Weld and the future of Seam | Dan Allen

64.
An event observer
Takes event API type with
Takes event API type with
public class GateServices { additional binding type
additional binding type
public void onIncomingFlight(
@Observes @Landing Flight flight,
Greeter greeter,
CateringService cateringService) {
Gate gate = ...;
flight.setGate(gate);
cateringService.dispatch(gate);
greeter.welcomeVisitors();
}
}
Additional parameters are
Additional parameters are
injected by the container
injected by the container
64 CDI (JSR-299), Weld and the future of Seam | Dan Allen

65.
Weld: JSR-299 Reference Implementation
● Developed under Seam project umbrella
● Version 1.0.1 available
● Bundled in JBoss AS 6 & GlassFish V3
● Support for Tomcat, Jetty & Java SE
● CDI enhancements & utilities for extension writers
● Maven archetypes for CDI & Java EE
65 CDI (JSR-299), Weld and the future of Seam | Dan Allen

66.
Seam’s mission statement
To provide a fully integrated development
platform for building rich Internet applications
based upon the Java EE environment.
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67.
Seam 3: Key themes
● Portability
● Portable extensions run on any CDI implementation
● Modularity (i.e., Seam à la carte)
● Module per integration
● Individual module leads
● Independent release cycles
● “Stack” releases
● Strong tooling
● Java compiler
● JBoss Tools
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68.
Seam's new modular ecosystem
68 CDI (JSR-299), Weld and the future of Seam | Dan Allen

69.
What's on the menu so far?
● Drools ● JavaScript Remoting
● JMS ● Security
● Faces ● Servlet
● International ● Wicket
● Persistence ● XML configuration
...and more
 http://sfwk.org/Seam3
69 CDI (JSR-299), Weld and the future of Seam | Dan Allen

70.
XML-based configuration
<beans ...
xmlns:app="java:urn:com.acme">
<app:TranslatingWelcome>
<app:Translating/>
<app:defaultLocale>en-US</app:defaultLocale>
</app:TranslatingWelcome>
</beans>
● Define, specialize or override beans
● Add annotations (qualifiers, interceptor bindings, ...)
● Assign initial property values
70 CDI (JSR-299), Weld and the future of Seam | Dan Allen

71.
End-to-end testing for Java EE
● SeamTest replacement
● ShrinkWrap
● Fluent API for creating Java archives
JavaArchive archive =
ShrinkWrap.create("archive.jar", JavaArchive.class)
.addClasses(MyClass.class, MyOtherClass.class)
.addResource("mystuff.properties");
● Arquillian
● Integration test harness
● Pluggable container support (embedded or remote)
● Supports injection into test class
● Tests can be run from IDE or build script
71 CDI (JSR-299), Weld and the future of Seam | Dan Allen

72.
72 CDI (JSR-299), Weld and the future of Seam | Dan Allen

73.
Summary
● JSR-299 provides a set of services for Java EE
● Bridges JSF and EJB
● Offers loose coupling with strong typing
● Catalyzed managed bean & interceptor specifications
● Extensive SPI for third-party integration with Java EE
● Weld: JSR-299 Reference Implementation
● Seam 3: Portable extensions for Java EE
73 CDI (JSR-299), Weld and the future of Seam | Dan Allen

74.
How do I get started with CDI or Java EE 6?
● Seam 3 project
http://seamframework.org/Seam3
● Weld Maven archetypes for CDI and Java EE
http://tinyurl.com/goweld
● Weld reference guide
http://tinyurl.com/weld-reference-101
● CDI JavaDoc
http://docs.jboss.org/cdi/api/latest/
● Any Java EE 6 container!
74 CDI (JSR-299), Weld and the future of Seam | Dan Allen

75.
Q&A
Dan Allen
Senior Software Engineer
JBoss, by Red Hat
http://in.relation.to
http://seamframework.org/Seam3