The document outlines a presentation by Alex Theedom on design patterns in Java EE, focusing on their historical context and practical applications in the framework. Key design patterns discussed include singleton, factory, façade, decorator, and observer, highlighting their implementations and the advantages and pitfalls associated with each. The session aims to provide insights into using these patterns effectively within the simplified Java EE programming model.

1. Java EE
revisits design patterns
Sep. 2-4
Kyiv, Desyatynna str. 12
@readlearncode
Alex Theedom Senior Java Developer

2. Who am I?
Alex Theedom, Senior Java Developer
@readlearncode

3. Available at

4. What’s on?
• Design patterns retrospective
• Map classical design patterns to Java EE 7
• Java EE Programming Model
• Singleton, Factory, Façade, Decorator and Observer
• Final Conclusions
• Q&A

5. The beginning
•Design Patterns: Elements of Reusable Object-Oriented Software
(E Gamma, R Helm, R Johnson and J Vlissides. 1994)
AKA Gang of Four AKA GoF
•Creational, behavioral and structural
•So what are design patterns in practice?

6. Enterprise Java and design
patterns
•JavaOne 2000 talk: Prototyping patterns for the J2EE
platform
•Core J2EE Patterns (D. Anur, J. Crupi and D. Malks)
•Out-of-box design pattern implementations with
Java EE 5

7. Java EE Programming Model
•Simplified programming model
•Annotations have replaced XML description files
•Convention over Configuration
•CDI hides object creation
•Resources are injected by type
•@Inject and disambiguation via custom qualifier
•POJO (JSR 299 managed bean)
•Otherwise @Produces

8. Singleton Pattern
•Creational pattern
•Single instance and instantiated once
•Must be thread safe
•Not normally destroy during application life cycle
•Classic implementation: private constructor, double
locking, static initializer, enums …

9. Singleton Pattern
@DependsOn("DatabaseConnectionBean")
@Startup
@Singleton
public class Logger {
@PostConstruct
void constructExpensiveObject() {
// Expensive construction
}
}
@DependsOn("DatabaseConnectionBean")
@Startup
@Singleton
public class Logger {
@PostConstruct
void constructExpensiveObject() {
// Expensive construction
}
}
@Inject
Logger logger;
@Inject
Logger logger;

10. Singleton Pattern
•Conclusions so far
•Very different implementation
•Substantially less boilerplate code
•Enhancements via specialized annotations
There’s more…

11. Singleton Pattern
@Singleton
@ConcurrencyManagement(ConcurrencyManagementType.BEAN)
public class Logger {
@AccessTimeout(value = 30, unit=TimeUnit.SECONDS)
@Lock(LockType.WRITE)
public void addMessage(String message) {}
@Lock(LockType.READ)
public String getMessage() {}
}
@Singleton
@ConcurrencyManagement(ConcurrencyManagementType.BEAN)
public class Logger {
@AccessTimeout(value = 30, unit=TimeUnit.SECONDS)
@Lock(LockType.WRITE)
public void addMessage(String message) {}
@Lock(LockType.READ)
public String getMessage() {}
}
•Container/bean managed concurrency

12. The Good, Bad and the Ugly
•The Good:
•enhancements via specialized annotations
•startup behavioural characteristics
•fine grain control over concurrency and access
timeout
•substantially less boilerplate code

13. The Good, Bad and the Ugly
•The Bad:
•overuse can cause problems
•lazy loading causes delays
•eager loading causes memory problems

14. •And the ugly:
•considered an anti-pattern
•only niche use
•smarter to use a stateless session bean
The Good, Bad and the Ugly

15. Factory Pattern
•Creational pattern
•Interface for creating family of objects
•Clients are decoupled from the creation

16. Factory Pattern
•CDI framework is a factory !?!
public class CoffeeMachine implements DrinksMachine {
// Implementation code
}
public class CoffeeMachine implements DrinksMachine {
// Implementation code
}
•Use it like so:
@Inject
DrinksMachine drinksMachine;
@Inject
DrinksMachine drinksMachine;

17. Factory Pattern
•Problem! Multiple concrete implementations
public class CoffeeMachine implements DrinksMachine {
// Implementation code
}
public class SoftDrinksMachine implements DrinksMachine {
// Implementation code
}
public class CoffeeMachine implements DrinksMachine {
// Implementation code
}
public class SoftDrinksMachine implements DrinksMachine {
// Implementation code
}
@Inject
DrinksMachine drinksMachine;
@Inject
DrinksMachine drinksMachine;
•Which DrinksMachine to inject?
?!?

18. Factory Pattern
•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

19. Factory Pattern
•Annotate respective classes
@Coffee
public class CoffeeMachine implements DrinksMachine {
// Implementation code
}
@Coffee
public class CoffeeMachine implements DrinksMachine {
// Implementation code
}
@SoftDrink
public class SoftDrinksMachine implements DrinksMachine {
// Implementation code
}
@SoftDrink
public class SoftDrinksMachine implements DrinksMachine {
// Implementation code
}

20. Factory Pattern
•Annotate injection points
@Inject @SoftDrink
DrinksMachine softDrinksMachine;
@Inject @SoftDrink
DrinksMachine softDrinksMachine;
@Inject @Coffee
DrinksMachine coffeeDrinksMachine;
@Inject @Coffee
DrinksMachine coffeeDrinksMachine;

21. Factory Pattern
•Remember
•Only JSR299 beans are ‘injectable’
•But I want to inject a Collection type or Object with a
parameterized constructor
-> let’s dive deeper

22. Factory Pattern
•Dive deeper
•Producer methods
•Use it like so:
@History
@Produces
public List<Book> getLibrary(){
// Generate a List of books called 'library'
return library;
}
@History
@Produces
public List<Book> getLibrary(){
// Generate a List of books called 'library'
return library;
}
@History
@Inject
List<Books> library;
@History
@Inject
List<Books> library;
@Qualifier
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface History
@Qualifier
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface History

23. Factory Pattern
•Scope
•Determines when method called
•Life of object: @RequestScoped -> @ApplicationScoped
@RequestScoped
@History
@Produces
public List<Book> getLibrary(){
// Generate a List of books called 'library'
return library;
}
@RequestScoped
@History
@Produces
public List<Book> getLibrary(){
// Generate a List of books called 'library'
return library;
}

24. The Good, Bad and the Ugly
•The Good:
•easy to implement
•no boilerplate code
•works magically
•any object can be made injectable
•automatic per class configuration
•Disambiguation/filtration via qualifiers

25. The Good, Bad and the Ugly
•The Bad: named annotation is not type safe
@Named("History") -> @History
•and the ugly: object creation hidden, hard to follow
execution flow, IDE should help

26. Façade Pattern
•Hides the complex logic and provides the interface for
the client
•Typically used in APIs
•Classic implementation: Just create a method to hide
complexity

27. Façade Pattern
•Encapsulates complicated logic
•@Stateless, @Stateful
@Stateless
public class BankServiceFacade{
public void complexBusinessLogic(){
// Very very complex logic
}
}
@Stateless
public class BankServiceFacade{
public void complexBusinessLogic(){
// Very very complex logic
}
}
@Inject
public BankServiceFacade service;
@Inject
public BankServiceFacade service;

28. The Good, Bad and the Ugly
•The Good: simple, robust, gives you a range of services
•The Bad: over use introduces unnecessary layers, if you
don’t need it don’t introduce one
•and the ugly: there isn’t one really

29. Decorator Pattern
•Structural Pattern
•Dynamically adds logic to an object at runtime
•More flexible that inheritance
•Classic implementation

30. Decorator Pattern
@Decorator
@Priority(Interceptor.Priority.APPLICATION)
public class PriceDiscountDecorator implements Product {
@Coffee
@Any
@Delegate
@Inject
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 {
@Coffee
@Any
@Delegate
@Inject
private Product product;
public String generateLabel() {
product.setPrice(product.getPrice() * 0.5);
return product.generateLabel();
}
}

31. •The Good: very easy to change behaviour without
breaking legacy code
•The Bad: needs XML config (<CDI 1.1)
•and the ugly: overuse will introduce an execution flow
which is hard to follow
The Good, Bad and the Ugly

32. Observer Pattern
•Behavioural Pattern
•Publisher-Subscriber
•Classic implementation: Implement a Subscriber
interface, register with publisher and call a notify
method on subscribers

33. Observer Pattern
•Define an event class
public class MessageEvent {
private String message;
public MessageEvent(String message){
this.message = message;
}
public String getMessage(){
return message;
}
}
public class MessageEvent {
private String message;
public MessageEvent(String message){
this.message = message;
}
public String getMessage(){
return message;
}
}

34. Observer Pattern
•Notifies dependents of state change
@Stateless
public class MessageService {
@Inject
Event<MessageEvent> messageEvent;
public void fireMessage(){
messageEvent.fire(new MessageEvent("Hello World"));
}
}
@Stateless
public class MessageService {
@Inject
Event<MessageEvent> messageEvent;
public void fireMessage(){
messageEvent.fire(new MessageEvent("Hello World"));
}
}

35. Observer Pattern
•Dependent receives state change notification
@Stateless
public class MessageObserver {
public void listenToMessage(@Observes MessageEvent message){
System.out.println(message.getMessage());
}
}
@Stateless
public class MessageObserver {
public void listenToMessage(@Observes MessageEvent message){
System.out.println(message.getMessage());
}
}

36. Observer Pattern
•Qualifier to filter events
@WarningMessage
@Inject
Event<MessageEvent> messageEvent;
@WarningMessage
@Inject
Event<MessageEvent> messageEvent;
public void listenToMessage(
@Observes @WarningMessage MessageEvent message)
public void listenToMessage(
@Observes @WarningMessage MessageEvent message)

37. The Good, Bad and the Ugly
•The Good: very easy, no boilerplate code, less than JMS,
the container does the heavy lifting, light weight
•The Bad: confusing execution order but IDE will help
•and the ugly: nothing, its beautiful

38. Final Conclusion
•Efficiency savings
•Greater control over behaviour
•New features enhance implementation

39. Q & A

40. Thank You
Sep. 2-4
Kyiv, Desyatynna str. 12
@readlearncode
Alex Theedom Senior Java Developer