Presenter Prasanna Kumar.S

Contexts and Dependency Injection (CDI)in JEE 6

JUGChennai JTech Day Sep'12

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

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

What is Dependency Injection

PHONE ==> SIM ==> TOWER

Why Dependency Injection

user just relies (on)ly the Phonestreamlining dependent objects injection by

“Don't call your service, let service call you”

Achieve loose coupling of objects

Well proven practise

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)

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

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

Basic CDI Beans

public interface Greeting {public String greet(String greet);

}

@Defaultpublic class PlainGreetingCDI implements Greeting {

public String greet(String greet) {return "greetings to " + greet;

}}

// client code@Injectprivate Greeting greeting;public String sayGreeting(String whomToGreet) {

return greeting.greet(whomToGreet);}

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 {

@Overridepublic Double convert(Double howMuchToConvert) {

return howMuchToConvert * 55;}

}

public enum VariousCurrencies { DOLLAR,EURO,POUNDS }

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 {

@Overridepublic Double convert(Double howMuchToConvert) {

return howMuchToConvert * 55;}

}

public enum VariousCurrencies { DOLLAR,EURO,POUNDS }

Qualifier in CDI (Contd)

// client code@Inject @CurrencyTypeprivate CurrencyConverter def_converter;

@Inject @CurrencyType(type=VariousCurrencies.EURO)private CurrencyConverter euroConverter;

Scoped Beans – Request Scope

@RequestScopedpublic 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);

}}

Scoped Beans – Request Scope

@Statelesspublic class ScopedCurrencyConverterEJB {

@Inject private RequestScopedCurrencyConverterCDI currencyConverterCDI@EJB private FormattedCurrencyConverter formattedCurrencyConverter;

public String getConvertedValue(double valueToConvert) {currencyConverterCDI.setCurrValue(valueToConvert);return formattedCurrencyConverter.getFormattedCurrency();

}}

@Stateless @LocalBeanpublic class FormattedCurrencyConverter {

@Inject private RequestScopedCurrencyConverterCDI currencyConverter;public String getFormattedCurrency() {

return "The converted "+ currencyConverter.getCurrValue() +" to " + currencyConverter.convert();

}}

Scoped Beans – Request Scope

// client code @EJBprivate ScopedCurrencyConverterEJB converterEJB;converterEJB.getConvertedValue(2) // "The converted 2.0 to 110.0"

Scoped Beans – Application Scope

@ApplicationScopedpublic class ApplicationScopedCDI {

private double currValue;

public void setCurrValue(double currValue) {this.currValue = currValue;

}

public double getCurrValue() {return currValue;

}

}// client codepublic void setValueToConvert(double value) {

applicationScopedCurrencyConverterCDI.setCurrValue(2);}

public double getValueToConvert() {return applicationScopedCurrencyConverterCDI.getCurrValue();

}

Scoped Beans – Application Scope

@ApplicationScopedpublic class ApplicationScopedCDI {

private double currValue;

public void setCurrValue(double currValue) {this.currValue = currValue;

}

public double getCurrValue() {return currValue;

}

}// client codepublic void setValueToConvert(double value) {

applicationScopedCurrencyConverterCDI.setCurrValue(2);}

public double getValueToConvert() {return applicationScopedCurrencyConverterCDI.getCurrValue();

}

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

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

Q&A