Beginning Java EE 6 with GlassFish 3, Second Edition

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CHAPTER 7 ■ SESSION BEANS AND THE TIMER SERVICEpublic List findBooks() {TypedQuery query = em.createNamedQuery("findAllBooks", Book.class);return query.getResultList();}public List findCDs() {TypedQuery query = em.createNamedQuery("findAllCDs", CD.class);return query.getResultList();}public Book createBook(Book book) {em.persist(book);return book;}}public CD createCD(CD cd) {em.persist(cd);return cd;}Stateless session beans often contain several closely related business methods. For example, theItemEJB bean in Listing 7-1 defines methods related to items sold by the CD-BookStore application. Soyou will find methods to create, update, or find books and CDs, as well as other related business logic.The @Stateless annotation marks the ItemEJB POJO as a stateless session bean, thus turning asimple Java class into a container-aware component. The specification of the @javax.ejb.Statelessannotation is described in Listing 7-2.Listing 7-2. @Stateless Annotation API@Target({TYPE}) @Retention(RUNTIME)public @interface Stateless {String name() default "";String mappedName() default "";String description() default "";}The name parameter specifies the name of the bean and by default is the name of the class (ItemEJBin the example in Listing 7-1). This parameter can be used to look up an EJB with JNDI, for example. Thedescription parameter is a string that can be used to describe the EJB. The mappedName attribute is theglobal JNDI name assigned by the container. Note that this JNDI name is vendor specific and is thereforenot portable. mappedName has no relationship with the portable global JNDI name, which I introduced inthe previous chapter and I’ll describe in detail later in the “Global JNDI Access” section.Stateless session beans can support a large number of clients, minimizing any needed resources.Having stateless applications is one way to improve scalability (as the container doesn’t have to storeand manage state).204
CHAPTER 7 ■ SESSION BEANS AND THE TIMER SERVICEStateful BeansStateless beans provide business methods to their clients but don’t maintain a conversational state withthem. Stateful session beans, on the other hand, preserve conversational state. They are useful for tasksthat have to be done in several steps, each of which relies on the state maintained in a previous step.Let’s take the example of a shopping cart in an e-commerce web site. A customer logs on (his sessionstarts), chooses a first book, adds it to his shopping cart, chooses a second book, and adds it to his cart.At the end, the customer checks out the books, pays for them, and logs out (the session ends). Theshopping cart keeps the state of how many books the customer has chosen throughout the interaction(which can take some time, specifically the time of the client’s session).Book book = new Book();book.setTitle("The Hitchhiker's Guide to the Galaxy");book.setPrice(12.5F);book.setDescription("Science fiction comedy series created by Douglas Adams.");book.setIsbn("1-84023-742-2");book.setNbOfPage(354);book.setIllustrations(false);statefulComponent.addBookToShoppingCart(book);book.setTitle("The Robots of Dawn");book.setPrice(18.25F);book.setDescription("Isaac Asimov's Robot Series");book.setIsbn("0-553-29949-2");book.setNbOfPage(276);book.setIllustrations(false);statefulComponent.addBookToShoppingCart(book);statefulComponent.checkOutShoppingCart();The preceding code shows exactly how a stateful session bean works. Two books are created andadded to a shopping cart of a stateful component. At the end, the checkOutShoppingCart() method relieson the maintained state and can check out the two books.When a client invokes a stateful session bean in the server, the EJB container needs to provide thesame instance for each subsequent method invocation. Stateful beans cannot be reused by other clients.Figure 7-3 shows the one-to-one correlation between a bean instance and a client. As far as thedeveloper is concerned, no extra code is needed, as this one-to-one correlation is managedautomatically by the EJB container.Figure 7-3. Clients accessing stateful beans205
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The EXPERT’s VOIce ® in Java tm
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Beginning Java EE 6 Platform with G
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Contents at a Glance■Foreword ...
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■ CONTENTSSummary ...............
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■ CONTENTSBulk Update ...........
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■ CONTENTSStateful . ............
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■ CONTENTSScripting Elements ....
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■ CONTENTSMDB Model .............
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■ CONTENTSFrom the Web to Web Ser
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About the Author■ Antonio Goncalv
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AcknowledgmentsWriting a book about
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■ PREFACECONTENTSChapter 1 briefl
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C H A P T E R 1■ ■ ■Java EE 6
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CHAPTER 1 ■ JAVA EE 6 AT A GLANCE
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CHAPTER 2 ■ JAVA PERSISTENCEJPA S
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CHAPTER 2 ■ JAVA PERSISTENCEEclip
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CHAPTER 2 ■ JAVA PERSISTENCEusing
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CHAPTER 3 ■ OBJECT-RELATIONAL MAP
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C H A P T E R 4■ ■ ■Managing
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CHAPTER 4 ■ MANAGING PERSISTENT O
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CHAPTER 9 ■ TRANSACTIONS AND SECU
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CHAPTER 10 ■ JAVASERVER FACESUnde
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CHAPTER 10 ■ JAVASERVER FACESorg.
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C H A P T E R 11■ ■ ■Pages an
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CHAPTER 11 ■ PAGES AND COMPONENTS
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CHAPTER 12 ■ PROCESSING AND NAVIG
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CHAPTER 13 ■ SENDING MESSAGESFigu
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CHAPTER 13 ■ SENDING MESSAGESJava
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CHAPTER 14 ■ SOAP WEB SERVICESFig
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CHAPTER 15 ■ RESTFUL WEB SERVICES
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■ INDEXApache Maven. See Mavenapp
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