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About Byron Kiourtzoglou

Byron Kiourtzoglou
Byron is a master software engineer working in the IT and Telecom domains. He is an applications developer in a wide variety of applications/services. He is currently acting as the team leader and technical architect for a proprietary service creation and integration platform for both the IT and Telecom industries in addition to a in-house big data real-time analytics solution. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.

Decorating classes at injection time with Java EE 6

Let’s say you have a ticket service that lets you order tickets for a certain event. The TicketService handles the registration etc, but we want to add catering. We don’t see this as part of the ticket ordering logic, so we created a decorator. The decorator will call the TicketService and add catering for the number of tickets.

The interface:

public interface TicketService {
    Ticket orderTicket(String name);
}


The implementation of the interface, creates a ticket and persists it.

@Stateless
public class TicketServiceImpl implements TicketService {
 
    @PersistenceContext
    private EntityManager entityManager;
 
    @TransactionAttribute
    @Override
    public Ticket orderTicket(String name) {

  Ticket ticket = new Ticket(name);

  entityManager.persist(ticket);

  return ticket;
    }
}


We create a new implementation of the same interface.

@Decorator
public class TicketServiceDecorator implements TicketService {
 
    @Inject
    @Delegate
    private TicketService ticketService;
    @Inject
    private CateringService cateringService;
 
    @Override
    public Ticket orderTicket(String name) {

  Ticket ticket = ticketService.orderTicket(name);

  cateringService.orderCatering(ticket);

  return ticket;
    }
}


We adjust our beans.xml to mark the TicketServiceDecorator as ‘Decorator’.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://java.sun.com/xml/ns/javaee"

 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/beans_1_0.xsd">
    <decorators>

  <class>be.styledideas.blog.decorator.TicketServiceDecorator</class>
    </decorators>
</beans>


We can combine a number of decorators and choose the order we want them executed.

<decorators>
    <class>be.styledideas.blog.decorator.HighDecorator</class>
    <class>be.styledideas.blog.decorator.LowDecorator</class>
</decorators>

Related Article:

Reference: Java EE6 Decorators, decorating classes at injection time from our JCG partner Jelle Victoor at Styled Ideas Blog

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