birt barcode tool Building business logic with session beans in Java

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Building business logic with session beans
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Figure 2.4 To make an otherwise overwhelming process manageable, the ActionBazaar ordering process is broken down into several steps. The first of these steps is to add one or more item to the order. The second step is to specify shipping information for the order. The third is to specify the billing information. Reviewing and confirming the order finishes the ordering process.
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Figure 2.4 depicts these ordering steps. With a stateful bean, the data the user enters at each step can be cached into bean variables until the ordering workflow completes, when the user confirms the order. Now that we know what we want, let s see how we can implement it. Implementing the solution Listing 2.3 shows a possible implementation of the ActionBazaar ordering workflow using a bean named PlaceOrderBean. As you can see, each of the ordering
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A first taste of EJB
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steps maps to a method in the PlaceOrderBean implementation. The addItem, setShippingInfo, setBillingInfo, and confirmOrder methods are called in sequence from the web tier in response to user actions in each step. The setBidderID method essentially represents an implicit workflow setup step. It is called at the beginning of the workflow behind the scenes by the web application to identify the currently logged-in user as the bidder placing the order. Except for the confirmOrder method, the remaining methods do little more than simply save user input into stateful instance variables. In a real application, of course, these methods would be doing a lot more, such as error handling, validation, figuring out the user s options for a given step, calculating costs, and so on. The confirmOrder method does several things using the data accumulated throughout the session: the complete order is saved into the database, the billing process is started in parallel, and an order ID is returned to the user as confirmation.
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Listing 2.3 PlaceOrderBean stateful session bean
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package ejb3inaction.example.buslogic; import javax.ejb.*; import java.util.ArrayList; import java.util.List;
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Marks POJO as stateful
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@Stateful public class PlaceOrderBean implements PlaceOrder { private Long bidderID; private List<Long> items; Defines stateful instance private ShippingInfo shippingInfo; variables private BillingInfo billingInfo;
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public PlaceOrderBean () { items = new ArrayList<Long>(); } public void setBidderID(Long bidderId) { this.bidderId = bidderId; } public void addItem(Long itemId) { items.add(itemId); } public void setShippingInfo(ShippingInfo shippingInfo) { this.shippingInfo = shippingInfo; }
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Building business logic with session beans
public void setBillingInfo(BillingInfo billingInfo) { this.billingInfo = billingInfo; }
Contains remove
method @Remove public Long confirmOrder() { Order order = new Order(); order.setBidderId(bidderId); order.setItems(items); order.setShippingInfo(shippingInfo); order.setBillingInfo(billingInfo);
saveOrder(order); billOrder(order); return order.getOrderId(); } ... } ... package ejb3inaction.example.buslogic; import javax.ejb.Remote; @Remote Defines remote business interface public interface PlaceOrder { void setBidderId(Long bidderId); void addItem(Long itemId); void setShippingInfo(ShippingInfo shippingInfo); void setBillingInfo(BillingInfo billingInfo); Long confirmOrder(); }
As you can see, overall there is no big difference between developing a stateless and a stateful bean. In fact, from a developer s perspective, the only difference is that the PlaceOrderBean class is marked with the @Stateful annotation instead of the @Stateless annotation b. As we know, though, under the hood this makes a huge difference in how the container handles the bean s relationship to a client and the values stored in the bean instance variables C. The @Stateful annotation also serves to tell the client-side developer what to expect from the bean if behavior is not obvious from the bean s API and documentation. It is also important to note the @Remove annotation D placed on the confirmOrder method. Although this annotation is optional, it is critical from a server performance standpoint.
A first taste of EJB
NOTE
The @Remove annotation marks the end of the workflow modeled by a stateful bean. In our case, we are telling the container that there is no longer a need to maintain the bean s session with the client after the confirmOrder method is invoked. If we didn t tell the container what method invocation marks the end of the workflow, the container could wait for a long time until it could safely time-out the session. Since stateful beans are guaranteed to be dedicated to a client for the duration of a session, this could mean a lot of orphaned state data consuming precious server resources for long periods of time!
There is virtually no difference between the bean interfaces for our stateless and stateful bean examples. Both are POJIs marked with the @Remote annotation to enable remote client access E. Let s now take a quick look at stateful beans from the client perspective. As you might expect, compared to stateless beans there are no major semantic differences.
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