Introduces JSR-299, the new Java standard for contextual lifecycle management, dependency injection (CDI) and event notification. Covers the core programming model, explains its relationship to EJB 3.1 and JSF 2.0, and clarifies how it unifies and enhances the Java EE platform as a whole (extending to JPA, JAX-RS and JMS). You are then introduced to Weld, the JSR-299 Reference Implementation, and its Servlet container and Java SE extensions. Finally, looks ahead at how a modularized Seam 3 ties into this new foundation as a set of portable CDI extensions.
JSR-299 (CDI), Weld and the Future of Seam: An Introduction to Contexts and Dependency Injection
1. JSR-299 (CDI), Weld and
the Future of Seam
Dan Allen
Principal Software Engineer
JBoss by Red Hat
2. Agenda
● Java EE today
● Where JSR-299 fits in
● JSR-299 themes
● CDI programming model tour
● CDI extensions
● Weld
● Seam 3
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3. Technology terminology
● JSR-299 (CDI)
● Contexts & Dependency Injection for the
Java EE Platform
● Weld
● JSR-299 Reference Implementation & TCK
● Extended CDI support (Servlets, Java SE)
● Portable CDI enhancements for extension writers
● Seam 3
● Portable extensions for Java EE
● Portable integrations with non-Java EE technologies
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4. What is Java EE?
● Standard platform comprised of
managed components & services
● Business logic as components
1. Less code
2. Higher signal-to-noise ratio
3. Powerful mechanisms for free
4. Portable knowledge
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5. Why reinvest?
Java EE 5
5
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6. Stated goal of JSR-299
Web tier Transactional tier
(JSF) (EJB)
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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
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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
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9. CDI: The big picture
● Fill in
● Catalyze
● Evolve
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10. Why dependency injection?
● Weakest aspect of Java EE 5
● Closed set of injectable resources
● @EJB
● @PersistenceContext, @PersistenceUnit
● @Resource (e.g., DataSource, UserTransaction)
● Name-based injection is fragile
● Lacked rules
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11. Leverage and extend Java’s type system
@Annotation <TypeParam>
This information is pretty useful!
Type
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12. 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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13. 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
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14. Strong typing
● Type-based injection
● Eliminate reliance on string-based names
● Refactor friendly
● 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 (optional)
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15. Who's bean is it anyway?
● Everyone throwing around this term “bean”
● JSF
● EJB
● Seam
● Spring
● Guice
● Web Beans
● Need a “unified bean definition”
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16. Managed bean specification
● Common bean definition
● Instances managed by Managed
the container Beans
● Common services
● Lifecycle callbacks
● Resource injections
● Interceptors JSF EJB CDI JAX-RS
● Foundation spec
How managed beans evolved: http://www.infoq.com/news/2009/11/weld10
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17. CDI bean ingredients
● Set of bean types
● Set of qualifiers
● Scope
● Bean EL name (optional)
● Set of interceptor bindings
● Alternative classification
● Bean implementation class
Auto-discovered!
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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() {
System.out.println(
w.buildPhrase("San Francisco"));
}
}
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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 + "!");
}
}
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25. Quiz: 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. Working out an ambiguous resolution
● Qualifier
● Alternative
● Producer
● Veto (or hide)
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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
@Qualifier
@Retention(RUNTIME)
@Target({TYPE, METHOD, FIELD, PARAMETER})
public @interface Translating {}
@interface means annotation
@interface means annotation
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29. Qualifying an implementation
@Translating
public class TranslatingWelcome extends Welcome {
@Inject GoogleTranslator translator;
public String buildPhrase(String city) {
return translator.translate(
"Welcome to " + city + "!");
}
}
● makes type more specific
● assigns semantic meaning
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30. Qualifier as a “binding type”
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31. Explicitly request qualified interface
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("San Francisco"));
}
}
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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
In other words, an override
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33. Defining an alternative
@Alternative
public class TranslatingWelcome extends Welcome {
@Inject GoogleTranslator translator;
public String buildPhrase(String city) {
return translator.translate(
"Welcome to " + city + "!");
}
}
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34. Substituting the alternative
● Activated using beans.xml
<beans>
<alternatives>
<class>com.acme.TranslatingWelcome</class>
</alternatives>
</beans>
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35. Assigning a bean (EL) 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("San Francisco"));
}
}
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36. Assigning a bean (EL) 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("San Francisco"));
}
}
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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
beans
CDI
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39. Stashing the bean in a context
● Bean saved for the duration of a request
@Named
@RequestScoped
public class Greeter {
@Inject private Welcome w;
private String city;
public String getCity() { return city; }
public void setCity(String city) {
this.city = city;
}
public void welcomeVisitors() {
System.out.println(w.buildPhrase(city));
}
}
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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>
San Francisco
Prints:
Welcome to San Francisco!
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41. Mission accomplished: We have a deal!
Web tier Business tier
(JSF) (managed bean)
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42. Scope types and contexts
● Default 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
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43. Scope transparency
● Scopes not visible to client (no coupling)
● Scoped beans are proxied for thread safety
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44. Conversation context
● Request ≤ Conversation ≪ Session
●
● Boundaries demarcated by application
● Optimistic transaction
● Conversation-scoped persistence context
● No fear of exceptions on lazy fetch operations
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45. 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();
}
...
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46. Controlling the conversation
...
public boolean confirm() {
if (!isValid()) {
return false;
}
em.persist(booking);
conversation.end();
return true;
}
}
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47. producer method
n. a method whose return value produces
an injectable object
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48. 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 Dynamic result set
Dynamic result set
public List<Product> getWishList() {
return em.createQuery("...").getResultList();
}
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49. Injecting producer return values
@Inject FacesContext ctx;
@Inject PaymentProcessor pp;
@Inject @WishList List<Product> wishlist;
Origin of product is hidden at injection point
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50. Bridging Java EE resources
● Use producer field to expose Java EE resource
@Stateless
public class UserEntityManagerProducer {
@Produces @UserRepository
@PersistenceContext(unitName = "users")
EntityManager em;
}
@Stateless
public class PricesTopicProducer {
@Produces @Prices
@Resource(name = "java:global/env/jms/Prices")
Topic pricesTopic;
}
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51. Injecting resources in type-safe way
● String-based resource names are hidden
public class UserManager {
@Inject @UserRepository EntityManager userEm;
...
}
public class StockDisplay {
@Inject @Prices Topic pricesTopic;
...
}
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52. Rethinking interceptors
@Interceptors(
SecurityInterceptor.class,
TransactionInterceptor.class,
LoggingInterceptor.class
)
@Stateful public class BusinessComponent {
...
}
Um, what's the point?
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53. Define an interceptor binding type
@InterceptorBinding
@Retention(RUNTIME)
@Target({TYPE, METHOD})
public @interface Secure {}
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54. Mark the interceptor implementation
@Secure
@Interceptor
public class SecurityInterceptor {
@AroundInvoke
public Object aroundInvoke(InvocationContext ctx)
throws Exception {
// enforce security...
ctx.proceed();
}
}
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55. Interceptor wiring with proper semantics
@Secure
public class AccountManager {
public boolean transfer(Account a, Account b) {
...
}
}
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56. 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
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57. Annotation jam!
@Secure
@Transactional
@RequestScoped
@Named
public class AccountManager {
public boolean transfer(Account a, Account b) {
...
}
}
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58. stereotype
n. an annotation used to group common
architectural patterns (recurring roles)
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59. Define a stereotype to bundle annotations
@Secure
@Transactional
@RequestScoped
@Named
@Stereotype
@Retention(RUNTIME)
@Target(TYPE)
public @interface BusinessComponent {}
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60. Using a stereotype
@BusinessComponent
public class AccountManager {
public boolean transfer(Account a, Account b) {
...
}
}
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61. Portable extensions
● SPI – Service Provider Interface
● Automatically discovered
● Application-scoped instance
● Observes events from CDI event bus
● Before/after bean discovery
● After deployment validation
● etc...
● Can override, augment, replace or veto beans
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62. 62 JSR-299 (CDI), Weld and the Future of Seam | Dan Allen
63. Weld: JSR-299 Reference Implementation
● Implementation & TCK
● Weld (portable) extensions
● Apache software licensed (version 2.0)
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65. 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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66. Seam’s new modular ecosystem
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67. Portable modules
● Module per domain or integration
● Independently...
● lead
● versioned
● released
● Per-module structure
● Based on CDI
● API & implementation
● Reference documentation & examples
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68. Stack releases
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69. What's on the menu so far?
● Drools ● JavaScript remoting
● jBPM ● Security
● JMS ● Servlet
● Faces ● Wicket
● International ● XML configuration
● Persistence ● Exception handling
...and more
http://github.com/seam
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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
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71. Cross-field validator in Seam Faces
@FacesValidator("addressValidator")
public class AddressValidator implements Validator {
@Inject Directory directory;
@Inject @InputField String city;
@Inject @InputField String state;
@Inject @InputField ZipCode zip;
public void validate(FacesContext ctx, UIComponent c,
Object v) throws ValidatorException {
if (!directory.exists(city, state, zip) {
throw new ValidatorException("Bad address");
}
}
}
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72. Wiring the validator to the inputs
<h:form id="address">
City: <h:inputText id="city" value="#{bean.city}"/>
State: <h:inputText id="state" value="#{bean.state}"/>
Zip: <h:inputText id="zipCode" value="#{bean.zip}"/>
<h:commandButton value="Update"
action="#{addressController.update}"/>
<s:validateForm validatorId="addressValidator"
fields="zip=zipCode">
</h:form>
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73. Arquillian: Container-oriented testing for Java EE
Throwing complexity over the wall
Throwing complexity over the wall
@RunWith(Arquillian.class)
Wed @ 4:45
Wed @ 4:45
public class GreeterTestCase { Hilton, Golden Gate 4/5
Hilton, Golden Gate 4/5
@Deployment
public static Archive<?> createDeployment() {
return ShrinkWrap.create(JavaArchive.class)
.addClasses(Greeter.class, GreeterBean.class);
}
@EJB private Greeter greeter;
@Test
public void shouldBeAbleToInvokeEJB() throws Exception {
assertEquals("Hello, Earthlings", greeter.greet("Earthlings"));
}
}
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74. Summary
● Java EE 6 is leaner and more productive
● JSR-299 (CDI) provides a set of services for Java EE
● Bridges JSF and EJB
● Offers loose coupling with strong typing
● Provides a type-based event bus
● Catalyzed managed bean & interceptor specifications
● Extensive SPI for third-party integration with Java EE
● Weld: JSR-299 reference implementation & add-ons
● Seam 3: Portable extensions for Java EE
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75. How do I get started?
● Download a Java EE 6 container
● JBoss AS 6 – http://jboss.org/jbossas
● GlassFish V3 – http://glassfish.org
● Generate a Java EE project using a Maven archetype
● http://tinyurl.com/goweld
● Read the Weld reference guide
● http://tinyurl.com/weld-reference-101
● Browse the CDI JavaDoc
● http://docs.jboss.org/cdi/api/latest/
● Check out the Seam 3 project
● http://seamframework.org/Seam3
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