this slide has been presented in JUGChennai JTechDay held on Sep 15 2012

1. Contexts and Dependency Injection (CDI)
in JEE 6
Presenter
Prasanna Kumar.S
JUGChennai JTech Day Sep'12

2. About me
A Java developer (now interested in Scala as well ...)
Active member in JUG Chennai
Creator & Co-Founder of scalaxia.com (a site which lists
out the popular tweets about scala)
Contributed for ScalaFX project
Contact
Mail me prassee.sathian@gmail.com
Follow me @prasonscala
I blog @ prasonscala@tumblr.com

3. Agenda
What is & Why DI ?
What is CDI
Features of CDI
Advantages of CDI
Injecting Beans (with some EJB tit-bits !!!)
Types of Injection
Qualifiers – Built in & custom qualifiers
Scope – Types of Scopes
CDI options....
Questions

4. What is Dependency Injection
PHONE ==> SIM ==> TOWER

5. Why Dependency Injection
user just relies (on)ly the Phone
streamlining dependent objects injection by
“Don't call your service,
let service call you”
Achieve loose coupling of objects
Well proven practise

6. What is CDI

JSR 299

Provides a unifying Dependency Injection and contextual life
cycle model for Java EE

A completely new, richer dependency management model

Type-safe dependency injection

Designed for use with stateful objects (scoped objects)

7. Advantages of CDI
Decouple server and client
– Using well-defined types and qualifiers
– Allows server implementations to vary
Decouple lifecycle of collaborating components
– Automatic contextual lifecycle
management by the CDI runtime
Decouple orthogonal concerns (AOP)
– Interceptors & Decorators
NO XML !!!!
Can be used in both JAVA SE and JAVA EE applications

8. Injecting Beans
CDI is all about DI
CDI makes use of annotations
3 Types of injection points

Field

Method Parameter
Methods can be

Constructor

Initializer

Setter

Producer

Observer

9. Basic CDI Beans
public interface Greeting {
public String greet(String greet);
}
@Default
public class PlainGreetingCDI implements Greeting {
public String greet(String greet) {
return "greetings to " + greet;
}
}
// client code
@Inject
private Greeting greeting;
public String sayGreeting(String whomToGreet) {
return greeting.greet(whomToGreet);
}

10. Qualifiers – Built in & custom quali-
fiers
public interface CurrencyConverter {
public Double convert(Double howMuchToConvert);
}
@Qualifier
@Retention(RUNTIME)
@Target({ TYPE, METHOD, FIELD, PARAMETER })
public @interface CurrencyType {
VariousCurrencies type() default VariousCurrencies.DOLLAR;
}
@CurrencyType(type = VariousCurrencies.DOLLAR)
public class DollarConverter implements CurrencyConverter {
@Override
public Double convert(Double howMuchToConvert) {
return howMuchToConvert * 55;
}
}
public enum VariousCurrencies { DOLLAR,EURO,POUNDS }

11. Qualifier in CDI
public interface CurrencyConverter {
public Double convert(Double howMuchToConvert);
}
@Qualifier
@Retention(RUNTIME)
@Target({ TYPE, METHOD, FIELD, PARAMETER })
public @interface CurrencyType {
VariousCurrencies type() default VariousCurrencies.DOLLAR;
}
@CurrencyType(type = VariousCurrencies.DOLLAR)
public class DollarConverter implements CurrencyConverter {
@Override
public Double convert(Double howMuchToConvert) {
return howMuchToConvert * 55;
}
}
public enum VariousCurrencies { DOLLAR,EURO,POUNDS }

12. Qualifier in CDI (Contd)
// client code
@Inject @CurrencyType
private CurrencyConverter def_converter;
@Inject @CurrencyType(type=VariousCurrencies.EURO)
private CurrencyConverter euroConverter;

13. Scoped Beans – Request Scope
@RequestScoped
public class RequestScopedCurrencyConverterCDI {
private double currValue;
@Inject
@CurrencyType(type=VariousCurrencies.DOLLAR)
private CurrencyConverter currencyConverter;
// setters and getter for currencyConverter
public double convert() {
return currencyConverter.convert(currValue);
}
}

14. Scoped Beans – Request Scope
@Stateless
public class ScopedCurrencyConverterEJB {
@Inject private RequestScopedCurrencyConverterCDI currencyConverterCDI
@EJB private FormattedCurrencyConverter formattedCurrencyConverter;
public String getConvertedValue(double valueToConvert) {
currencyConverterCDI.setCurrValue(valueToConvert);
return formattedCurrencyConverter.getFormattedCurrency();
}
}
@Stateless @LocalBean
public class FormattedCurrencyConverter {
@Inject private RequestScopedCurrencyConverterCDI currencyConverter;
public String getFormattedCurrency() {
return "The converted "+ currencyConverter.getCurrValue() +" to " +
currencyConverter.convert();
}
}

15. Scoped Beans – Request Scope
// client code
@EJB
private ScopedCurrencyConverterEJB converterEJB;
converterEJB.getConvertedValue(2) // "The converted 2.0 to 110.0"

16. Scoped Beans – Application Scope
@ApplicationScoped
public class ApplicationScopedCDI {
private double currValue;
public void setCurrValue(double currValue) {
this.currValue = currValue;
}
public double getCurrValue() {
return currValue;
}
}
// client code
public void setValueToConvert(double value) {
applicationScopedCurrencyConverterCDI.setCurrValue(2);
}
public double getValueToConvert() {
return applicationScopedCurrencyConverterCDI.getCurrValue();
}

17. Scoped Beans – Application Scope
@ApplicationScoped
public class ApplicationScopedCDI {
private double currValue;
public void setCurrValue(double currValue) {
this.currValue = currValue;
}
public double getCurrValue() {
return currValue;
}
}
// client code
public void setValueToConvert(double value) {
applicationScopedCurrencyConverterCDI.setCurrValue(2);
}
public double getValueToConvert() {
return applicationScopedCurrencyConverterCDI.getCurrValue();
}

18. CDI options
Reference Implementations
JBoss Weld
http://seamframework.org/Weld
Apache OpenWebBeans
http://openwebbeans.apache.org/owb/indexhtml
Caucho
http://www.caucho.com/
Supported App Containers
Jboss AS 7,GlassFish 3.1x ,Caucho, TomEE !!! &
all JEE6 containers

19. How do I learn / adopt
All code presented here are available under
https://github.com/prassee/JTechDayCDIExamples
You are welcome to contribute your own examples -
(Shameless sales pitch !!!!)
Project using CDI
AGORAVA project - http://agorava.org/
Feel free to contribute
JavaPassion site
http://javapassion.com/jugtalks
TomEE examples Trunk
http://tomee.apache.org/examples-trunk/index.html

20. Q&A