CDI, Weld and the future of Seam

CDI (JSR-299), Weld and
the future of Seam

Dan Allen
Senior Software Engineer
JBoss by Red Hat

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

Agenda

● Terminology
● Why JSR-299?
● JSR-299 themes
● Brief tour of programming model
● Weld
● Seam


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


Stated goal of JSR-299

Web tier Transactional tier
(JSF) (EJB)


Why reinvest?
Java EE 5

6
Seam 2 CDI (JSR-299), Weld and the future of Seam | Dan Allen

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


CDI: The big picture

● Fill in
● Catalyze
● Evolve


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


JSR-299 theme

@Produces @WishList
Loose coupling... List<Product> getWishList()

Event<Order>
@InterceptorBinding
@Inject @UserDatabase EntityManager
@Observes
@Qualifier ...with strong typing


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

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


Leverage and extend Java’s type system

@Annotation <TypeParam>

This information is pretty useful!

Type


Who's bean is it anyway?

● Everyone throwing around this term “bean”
● JSF
● EJB
● Seam
● Spring
● Guice
● CDI
● Need a “unified bean definition”


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

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


Welcome to CDI, managed beans!

public class Welcome {
public String buildPhrase(String city) {
return "Welcome to " + city + "!";
}
}


Welcome to CDI, EJB 3.1 session beans!

@Stateless public class Welcome {
}
}


When is a bean recognized?

● Bean archive (WAR) ● Bean archive (JAR)

beans.xml can be empty!


Injection 101

public class Greeter {
@Inject Welcome w;

public void welcome() { @Default qualifier implied
@Default qualifier implied
System.out.println(
w.buildPhrase("Reston"));
}
}


Where can it be injected?

● Field
● Method parameter
● Constructor*
● Initializer
● Producer
● Observer


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


The bean vs “the other implementation”

● Multiple implementations of same interface
● One implementation extends another
public class Welcome {
}
}

public class TranslatingWelcome extends Welcome {

@Inject GoogleTranslator translator;

return translator.translate(
"Welcome to " + city + "!");
}
}

Quiz: Now which implementation gets injected?

private Welcome welcome;

@Inject
void init(Welcome welcome) {
this.welcome = welcome;
}

...
}

It's ambiguous!


Settling an ambiguous resolution

● Qualifier
● Alternative
● Hide bean types


qualifier

n. an annotation used to resolve an API
implementation variant at an injection point


Defining a qualifier

● A qualifier is an annotation
@Qualifier
@Retention(RUNTIME)
@Target({TYPE, METHOD, FIELD, PARAMETER})
public @interface Translating {}


Qualifying an implementation

● Adding a qualifier annotation:
● makes type more specific
● assigns semantic meaning
@Translating


}
}


Qualifier as a “binding type”


Using a specific implementation

● Qualified implementation must be requested explicitly
● Akin to the factory method pattern
● Resolves ambiguity at injection point!
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"));
}
}

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


Defining an alternative

@Alternative


}
}


Substituting the alternative

● Implementation must be activated using beans.xml
<beans>
<alternatives>
<class>com.acme.TranslatingWelcome</class>
</alternatives>
</beans>


Assigning a bean name

@Named("greeter")

@Inject
}

System.out.println(
}
}


Assigning a bean name by convention

@Named
private Welcome welcome; Bean name is decapitalized
Bean name is decapitalized
simple class name
simple class name
@Inject
}

System.out.println(
}
}


Welcome to CDI, JSF!

● Use the bean directly in the JSF view
<h:form>
<h:commandButton value="Welcome visitors"
action="#{greeter.welcomeVisitors}"/>
</h:form>


JSF
managed JSP
beans

CDI Facelets


Stashing the bean in a context

● Bean saved for the duration of a request
@RequestScoped
@Named("greeter")
private String city; // getter and setter hidden

@Inject
this.welcome = welcome
}

System.out.println(welcome.buildPhrase(city));
}
}


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


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

Scope transparency

● Scopes not visible to client
● No coupling between scope and use of type
● Scoped beans are proxied for thread safety


Conversation context

● Request <= Conversation << Session

●

● Boundaries demarcated by application

● Optimistic transaction
● Conversation-scoped persistence context
● No fear of exceptions on lazy fetch operations


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();
}

...


Controlling the conversation

...

public boolean confirm() {
if (!isValid()) {
return false;
}

em.persist(booking);
conversation.end();
return true;
}
}


producer method

n. a method whose return value produces
an injectable object


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();
}


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;
}


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;
...
}


Rethinking interceptors

@Interceptors(
SecurityInterceptor.class,
TransactionInterceptor.class,
LoggingInterceptor.class
)
@Stateful public class BusinessComponent {
...
}

Um, what's the point?


Interceptor wiring in JSR-299 (1)

● Define an interceptor binding type
@InterceptorBinding
@Retention(RUNTIME)
@Target({TYPE, METHOD})
public @interface Secure {}



● Marking the interceptor implementation
@Secure
@Interceptor
public class SecurityInterceptor {

@AroundInvoke
public Object aroundInvoke(InvocationContext ctx)
throws Exception {
// ...enforce security...
ctx.proceed();
}

}



● Applying interceptor with proper semantics
@Secure
public class AccountManager {

public boolean transfer(Account a, Account b) {
...
}

}


Multiple interceptors

● Application developer only concerned about semantics
@Transactional
public class AccountManager {

@Secure
...
}

}


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


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 {}


Multiple interceptors (but you won’t know it)

● Interceptors inherited from composite binding types
public
@BusinessOperation
class AccountManager {

...
}

}


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


Annotation jam!

● Without stereotypes, annotations pile up
public
@Secure
@Transactional
@RequestScoped
@Named

...
}

}


Defining a stereotype

● Stereotypes are annotations that group annotations
public
@Secure
@Transactional
@RequestScoped
@Named
@Stereotype
@Retention(RUNTIME)
@Target(TYPE)
@interface BusinessComponent {}


Using a stereotype

● Stereotypes give a clear picture, keep things simple
public
@BusinessComponent

...
}

}


Events

● Completely decouple action and reactions
● Selectors tune which event notifications are received
● Can be observed:
● immediately,
● after transaction completion or
● asynchronously (via extension)


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));
}
}


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


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


Seam’s mission statement

To provide a fully integrated development
platform for building rich Internet applications
based upon the Java EE environment.


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

Seam's new modular ecosystem


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


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


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

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


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!


Q&A

Dan Allen
Senior Software Engineer
JBoss, by Red Hat

http://in.relation.to
http://seamframework.org/Seam3

CDI, Weld and the future of Seam

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