Devoxx UK 2015: How Java EE has changed pattern implementation

@alextheedom@alextheedom#JavaEE#JavaEE

Professional Java EE Design PatternsProfessional Java EE Design Patterns

Alex Theedom@alextheedom alextheedom.com

Alex Theedom@alextheedom alextheedom.com


Speaker’s BioSpeaker’s Bio

•Senior Java Developer

•Author: Professional Java EE Design Patterns

•E-learning Platforms

•Cash Machine Software

•Microservice Based Lottery Systems

•Spring and Java EE


What to expectWhat to expect

•What’s the story

•Deep Dive

•Singleton Pattern

•Factory Pattern

•Quickie Patterns

•Façade, Decorator, Observer and more…


What’s the storyWhat’s the story

•Java EE changed design pattern implementation

• Implementation has simplified

• Implementation has been enhanced

•Greater creativity


Singleton PatternSingleton Pattern

•Ubiquitous and controversial but inescapable

•Instantiated once

•Not normally destroyed during application life cycle


Conventional ImplementationConventional Implementation

public class Logger { private static Logger instance; private Logger() { // Creation code here }

public static synchronized Logger getInstance() { if(instance == null) { instance = new Logger(); } return instance; } }

public class Logger { private static Logger instance; private Logger() { // Creation code here }

public static synchronized Logger getInstance() { if(instance == null) { instance = new Logger(); } return instance; } }


Conventional ImplementationConventional Implementation

•Only one instance of Logger created

•Created by first call to getInstance()

•Thread safe creation

•Use it like so:

Logger logger = Logger.getInstance(); Logger logger = Logger.getInstance();


Java EE ImplementationJava EE Implementation @Singleton public class Logger {

private Logger() { // Creation code here }

}

@Singleton public class Logger {


}


Java EE ImplementationJava EE Implementation

•Only one instance of Logger created

•Created by container (lazily)

•Knows it’s a singleton because @Singleton

•Use it like so:

@Inject Logger logger; @Inject Logger logger;



•Eager instantiation @Startup

•Perform startup tasks @PostConstruct



@Startup @Singleton public class Logger {


@PostConstruct void startUpTask() { // Perform start up tasks } }

@Startup @Singleton public class Logger {


@PostConstruct void startUpTask() { // Perform start up tasks } }



•Specify dependent instantiation

@DependsOn("MyBean") @Startup @Singleton public class Logger { ... }

@DependsOn("MyBean") @Startup @Singleton public class Logger { ... }



@DependsOn("MyBean") @Startup @Singleton public class Logger{

private Logger(){ // Creation code here }

@PostConstruct void startUpTask(){ // Perform start up tasks } }

@DependsOn("MyBean") @Startup @Singleton public class Logger{

private Logger(){ // Creation code here }

@PostConstruct void startUpTask(){ // Perform start up tasks } }



•Conclusions so far

•Very different implementation

•Substantially less boilerplate code

•Enhancements via specialized annotations



•Further enhancements

•Fine grain concurrency management

•Container vs. bean managed

@Singleton @ConcurrencyManagement(ConcurrencyManagementType.BEAN) public class Logger { ... }

@Singleton @ConcurrencyManagement(ConcurrencyManagementType.BEAN) public class Logger { ... }

•What about method access?


Java EE ImplementationJava EE Implementation•Method access

•LockType.WRITE and LockType.READ

•Method access timeout

@AccessTimeout(value = 30, unit=TimeUnit.SECONDS) @Lock(LockType.WRITE) public void addMessage(String message) { // Add message to log }

@Lock(LockType.READ) public String getMessage() { // Get message }

@AccessTimeout(value = 30, unit=TimeUnit.SECONDS) @Lock(LockType.WRITE) public void addMessage(String message) { // Add message to log }

@Lock(LockType.READ) public String getMessage() { // Get message }


ConclusionConclusion

•Substantially different manner of implementation

•Marked reduction in code

•Implementation improved via specialized annotations

•Startup behavioural characteristics

•Fine grain control over concurrency and access timeout


Factory PatternFactory Pattern

•Creational pattern

•Interface for creating family of objects

•Clients are decoupled from the creation



•CDI framework is a factory

public class CoffeeMachine implements DrinksMachine {} public class CoffeeMachine implements DrinksMachine {}

•Use it like so:

@Inject DrinksMachine drinksMachine; @Inject DrinksMachine drinksMachine;



•Problem! Multiple concrete implementations

public class CoffeeMachine implements DrinksMachine{…}

public class SoftDrinksMachine implements DrinksMachine{…}

public class CoffeeMachine implements DrinksMachine{…}

public class SoftDrinksMachine implements DrinksMachine{…}

@Inject DrinksMachine drinksMachine; @Inject DrinksMachine drinksMachine;

•Which DrinksMachine to inject?



•Solution! Qualifiers

@Qualifier @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.METHOD, ElementType.FIELD}) public @interface SoftDrink

@Qualifier @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.METHOD, ElementType.FIELD}) public @interface SoftDrink

@Qualifier @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.METHOD, ElementType.FIELD}) public @interface Coffee

@Qualifier @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.METHOD, ElementType.FIELD}) public @interface Coffee


Java EE ImplementationJava EE Implementation•Annotate respective classes

@Coffee public class CoffeeMachine implements DrinksMachine {} @Coffee public class CoffeeMachine implements DrinksMachine {}

@SoftDrink public class SoftDrinksMachine implements DrinksMachine {} @SoftDrink public class SoftDrinksMachine implements DrinksMachine {}

•Annotate injection points @Inject @SoftDrink DrinksMachine softDrinksMachine; @Inject @SoftDrink DrinksMachine softDrinksMachine;

@Inject @Coffee DrinksMachine coffeeDrinksMachine; @Inject @Coffee DrinksMachine coffeeDrinksMachine;



•Conclusions so far

•No boilerplate code

•Container does all the hard work

•Disambiguation via qualifiers

•Remember

•Only JSR299 beans are ‘injectable’



•Dive deeper

•Producer methods

•Use it like so:

@Produces @Library public List<Book> getLibrary(){ // Generate a List of books called 'library' return library; }

@Produces @Library public List<Book> getLibrary(){ // Generate a List of books called 'library' return library; }

@Inject @Library List<Books> library; @Inject @Library List<Books> library;



•Scope

•Determines when method called

•Life of object: @RequestScoped -> @ApplicationScoped @RequestScoped @Produces @Library public List<Book> getLibrary(){ // Generate a List of books called 'library' return library; }

@RequestScoped @Produces @Library public List<Book> getLibrary(){ // Generate a List of books called 'library' return library; }


Java EE ImplementationJava EE Implementation•Parameterized creation

•Use it like so:

public class LoggerFactory{ @Produces public Logger logger(InjectionPoint injectionPoint) { return Logger.getLogger( injectionPoint.getMember() .getDeclaringClass().getName()); } }

public class LoggerFactory{ @Produces public Logger logger(InjectionPoint injectionPoint) { return Logger.getLogger( injectionPoint.getMember() .getDeclaringClass().getName()); } }

@Inject private transient Logger logger; @Inject private transient Logger logger;


ConclusionConclusion

•CDI removes need for factory pattern

•Container does all the hard work

•Substantially less boilerplate code

•Disambiguation via qualifiers

•Virtually any object can be made injectable

•Automatic per class configuration


Other PatternsOther Patterns

•Façade

•Decorator

•Observer

•and more…


Façade PatternFaçade Pattern•Encapsulates complicated logic

•@Stateless, @Stateful

@Stateless public class BankServiceFacade { @Inject private AccountService accountService;

}

@Stateless public class BankServiceFacade { @Inject private AccountService accountService;

}

@Stateless public class AccountService{} @Stateless public class AccountService{}


Decorator PatternDecorator Pattern

•Dynamically adds logic to an object


Decorator PatternDecorator Pattern

@Decorator @Priority(Interceptor.Priority.APPLICATION) public class PriceDiscountDecorator implements Product {

@Any @Inject @Delegate private Product product;

public String generateLabel() { product.setPrice(product.getPrice() * 0.5); return product.generateLabel(); } }

@Decorator @Priority(Interceptor.Priority.APPLICATION) public class PriceDiscountDecorator implements Product {

@Any @Inject @Delegate private Product product;

public String generateLabel() { product.setPrice(product.getPrice() * 0.5); return product.generateLabel(); } }


Observer PatternObserver Pattern

•Notifies dependents of state change

public void trace(@Observes String message){ // Response to String event }

public void trace(@Observes String message){ // Response to String event }


Final ConclusionFinal Conclusion

•Efficiency savings

•Greater control over behaviour

•New features enhance implementation

•Opens doors to new pattern design

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Devoxx UK 2015: How Java EE has changed pattern implementation