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Building business logic with session beans
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Before we jump into analyzing code, let s briefly discuss the ActionBazaar business logic that we ll implement as a stateless session bean.
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3.2.1 The BidManagerBean example
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Bidding is a critical part of the ActionBazaar functionality. Users can bid on an item and view the current bids, while ActionBazaar administrators and customer service representatives can remove bids under certain circumstances. Figure 3.4 depicts these bid-related actions. Because all of these bid-related functions are simple, single-step processes, a stateless session bean can be used to model all of them. The BidManagerBean presented in listing 3.1 contains methods for adding, viewing, and canceling (or removing) bids. This is essentially an enhanced, more realistic version of the basic PlaceBid EJB we saw earlier. The complete code is available for download from www.manning.com/panda in the zip containing code examples.
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Figure 3.4 Some ActionBazaar bid-related actions. While bidders can place bids and view the current bids on an item, admins can remove bids when needed. All of these actions can be modeled with a singe stateless session bean.
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Stateless session beans
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We are using JDBC for simplicity only because we have not introduced the EJB 3 Java Persistence API (JPA) in any detail quite yet, and we don t assume you already understand ORM. Using JDBC also happens to demonstrate the usage of dependency injection of resources and the stateless bean lifecycle callbacks pretty nicely! In general, you should avoid using JDBC in favor of JPA once you are comfortable with it.
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Listing 3.1 Stateless session bean example
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@Stateless(name="BidManager") Marks as stateless bean public class BidManagerBean implements BidManager { @Resource(name="jdbc/ActionBazaarDS") private DataSource dataSource; Injects data source private Connection connection; ... public BidManagerBean() {}
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Receives PostConstruct
callback @PostConstruct public void initialize() { try { connection = dataSource.getConnection(); } catch (SQLException sqle) { sqle.printStackTrace(); } }
public void addBid(Bid bid){ try { Long bidId = getBidId(); Statement statement = connection.createStatement(); statement.execute( "INSERT INTO BIDS (" + "BID_ID, " + "BID_AMOUNT, " + "BID_BIDDER_ID, " + "BID_ITEM_ID) " + "VALUES (" + bidId + ", " + bid.getAmount() + ", " + bid.getBidder().getUserId() + ", " + bid.getItem().getItemId()+ ")"); } catch (Exception e) { e.printStackTrace(); } }
Receives PreDestroy callback
@PreDestroy public void cleanup() {
Building business logic with session beans
try { connection.close(); } catch (SQLException sqle) { sqle.printStackTrace(); } }
private Long getBidId() { ... } public void cancelBid(Bid bid) {...} public List<Bid> getBids(Item item) {...} ... } Designates remote ... business interface @Remote public interface BidManager { void addBid(Bid bid); void cancelBid(Bid bid); List<Bid> getBids(Item item); }
As you ve seen before, the @Stateless annotation marks the POJO as a stateless session bean b. The BidManagerBean class implements the BidManager interface, which is marked @Remote F. We use the @Resource annotation to perform injection of a JDBC data source C. The BidManagerBean has a no-argument constructor that the container will use to create instances of BidManagerBid EJB object. The PostConstruct D and PreDestroy E callbacks are used to manage a JDBC database connection derived from the injected data source. Finally, the addBid business method adds a bid into the database. We ll start exploring the features of EJB 3 stateless session beans by analyzing this code next, starting with the @Stateless annotation.
3.2.2 Using the @Stateless annotation
The @Stateless annotation marks the BidManagerBean POJO as a stateless session bean. Believe it or not, other than marking a POJO for the purposes of making the container aware of its purpose, the annotation does not do much else. The specification of the @Stateless annotation is as follows:
@Target(TYPE) @Retention(RUNTIME) public @interface Stateless { String name() default "";
Stateless session beans
String mappedName() default ""; String description() default ""; }
The single parameter, name, specifies the name of the bean. Some containers use this parameter to bind the EJB to the global JNDI tree. Recall that JNDI is essentially the application server s managed resource registry. All EJBs automatically get bound to JNDI as soon as they catch the container s watchful eye. You ll see the name parameter in use again in chapter 11 when we discuss deployment descriptors. In listing 3.1, the bean name is specified as BidManager. As the annotation definition shows, the name parameter is optional since it is defaulted to an empty String. We could easily omit it as follows:
@Stateless public class BidManagerBean implements BidManager {
If the name parameter is omitted, the container assigns the name of the class to the bean. In this case, the container assumes the bean name is BidManagerBean. mappedName is a vendor-specific name that you can assign to your EJB; some containers, such as the GlassFish application server, use this name to assign the global JNDI name for the EJB. As we noted, the BidManagerBean implements a business interface named BidManager. Although we ve touched on the idea of a business interface, we haven t dug very deeply into the concept. This is a great time to do exactly that.
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