Enterprise JavaBeans 3.0, 5th Edition

Chapter 16. Transactions

ACID Transactions

To understand how transactions work, we will revisit the TravelAgent EJB, the stateful session bean developed in Chapter 11 that encapsulates the process of making a cruise reservation for a customer. The TravelAgent EJB’s bookPassage( ) method looks like this:

public TicketDO bookPassage(CreditCardDO card, double price)
    throws IncompleteConversationalState {

    if (customer == null || cruise == null || cabin == null) {
        throw new IncompleteConversationalState( );
    }
    try {
        Reservation reservation = new Reservation(
            customer, cruise, cabin, price);
        entityManager.persist(reservation);

        this.processPayment.byCredit(customer, card, price);

        TicketDO ticket = new TicketDO(customer,cruise,cabin,price);

        return ticket;
    } catch(Exception e) {
        throw new EJBException(e);
    }
}

The TravelAgent EJB is a fairly simple session bean, and its use of other EJBs is typical of business-object design and taskflow. Unfortunately, good business-object design is not enough to make these EJBs useful in an industrial-strength application. The problem is not with the definition of the EJBs or the taskflow; the problem is that a good design does not, in and of itself, guarantee that the TravelAgent EJB’s bookPassage( ) method represents a good transaction. To understand why, we will take a closer look at what a transaction is and what criteria a transaction must meet to be considered reliable.

In business, a transaction usually involves an exchange between two parties. When ...