birt barcode tool New features: simplifying EJB in Java

Creation ECC200 in Java New features: simplifying EJB

New features: simplifying EJB
Data Matrix ECC200 Creator In Java
Using Barcode generator for Java Control to generate, create DataMatrix image in Java applications.
www.OnBarcode.com
Data Matrix Scanner In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Table 2.1 Major metadata annotations introduced in Java EE. Although primarily geared toward EJB, these annotations apply to Java EE components such as servlets and JSF managed beans as well as application clients. Annotations defined in the javax.annotation.* package are defined by the Common Metadata Annotations API (JSR-250). Annotations javax.annotation.Resource Usage Dependency injection of resources such as DataSource, JMS objects, etc. Dependency injection of session beans Dependency injection of web services Dependency injection of container-managed EntityManager Dependency injection of EntityManagerFactory Lifecycle method Lifecycle method Security Security Components That Can Use Them EJB, web, application client
Code 128 Code Set B Encoder In Java
Using Barcode generator for Java Control to generate, create Code 128B image in Java applications.
www.OnBarcode.com
Encoding Matrix 2D Barcode In Java
Using Barcode creator for Java Control to generate, create Matrix image in Java applications.
www.OnBarcode.com
javax.ejb.EJB
Linear Encoder In Java
Using Barcode maker for Java Control to generate, create 1D Barcode image in Java applications.
www.OnBarcode.com
Barcode Generator In Java
Using Barcode creator for Java Control to generate, create Barcode image in Java applications.
www.OnBarcode.com
EJB, web, application client EJB, web, application client EJB, web
Encoding EAN128 In Java
Using Barcode generation for Java Control to generate, create UCC.EAN - 128 image in Java applications.
www.OnBarcode.com
Drawing Code 93 In Java
Using Barcode creator for Java Control to generate, create Code 93 Full ASCII image in Java applications.
www.OnBarcode.com
javax.jws.WebServiceRef
Data Matrix ECC200 Decoder In Visual Basic .NET
Using Barcode recognizer for VS .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
ECC200 Generator In Java
Using Barcode generator for Java Control to generate, create ECC200 image in Java applications.
www.OnBarcode.com
javax.persistence.PersistenceContext
UCC.EAN - 128 Printer In None
Using Barcode maker for Excel Control to generate, create EAN / UCC - 14 image in Microsoft Excel applications.
www.OnBarcode.com
UCC - 12 Creator In Visual C#
Using Barcode creation for .NET Control to generate, create GS1 - 12 image in VS .NET applications.
www.OnBarcode.com
javax.persistence.PersistenceUnit
Recognize Code 128A In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
QR Code 2d Barcode Encoder In Java
Using Barcode generator for Android Control to generate, create QR Code ISO/IEC18004 image in Android applications.
www.OnBarcode.com
EJB, web
Create EAN-13 In Java
Using Barcode generation for Eclipse BIRT Control to generate, create GS1 - 13 image in BIRT reports applications.
www.OnBarcode.com
Creating QR Code ISO/IEC18004 In Objective-C
Using Barcode generator for iPad Control to generate, create QR Code JIS X 0510 image in iPad applications.
www.OnBarcode.com
javax.annotation.PostConstruct javax.annotation.PreDestroy javax.annotation.security.RunAs javax.annotation.security. RolesAllowed javax.annotation.security.PermitAll javax.annotation.security.DenyAll javax.annotation.security. DeclareRoles
Barcode Decoder In Java
Using Barcode Control SDK for Eclipse BIRT Control to generate, create, read, scan barcode image in BIRT reports applications.
www.OnBarcode.com
Paint Data Matrix In Objective-C
Using Barcode printer for iPhone Control to generate, create ECC200 image in iPhone applications.
www.OnBarcode.com
EJB, web EJB, web EJB, web EJB
Draw QR Code In .NET
Using Barcode encoder for Reporting Service Control to generate, create QR Code JIS X 0510 image in Reporting Service applications.
www.OnBarcode.com
Encode USS Code 39 In Visual Studio .NET
Using Barcode generator for Reporting Service Control to generate, create USS Code 39 image in Reporting Service applications.
www.OnBarcode.com
Security Security Security
EJB EJB EJB, web
As you can see, dependency injection is front and center of the common metadata annotations, including the @Resource, @EJB, @WebServiceRef, @PersistenceContext, and @PersistenceUnit annotations. Just as metadata annotations take the ugliness of descriptors away from the developer s view, dependency injection solves the complexities surrounding manual JNDI lookups. Let s take a look at this concept next.
A first taste of EJB
2.1.2 Introducing dependency injection
Almost every component uses another component or resource to implement functionality. The primary goal of dependency injection (DI) is to make component interdependencies as loosely coupled as possible. In real terms, this means that one component should call another component or resource only through an interface and that components and resources should be glued together using configuration instead of code. As a result, component implementations can easily be swapped out as necessary simply by reconfiguring the application. If you ve used JNDI extensively in EJB 2, you ll appreciate how much this means. We won t talk about JNDI very much here since in most cases you can get away without knowing anything about it. If you don t know about JNDI and are curious to learn more, we discuss it in some length in appendix A. Figure 2.1 shows the difference between manual JNDI lookups and DI. In a sense, injection is lookup reversed. As you can see, in the manual JNDI lookup model, the bean explicitly retrieves the resources and components it needs. As a result, component and resource names are hard-coded in the bean. With DI, on the other hand, the container reads target bean configuration, figures out what beans and resources the target bean needs, and injects them into the
Figure 2.1 When you re using JNDI, it s the responsibility of the client to do a lookup and obtain a reference to the object. In EJB 3, you may think dependency injection is the opposite of JNDI. It is the responsibility of the container to inject an object based on the dependency declaration.
Introducing the ActionBazaar application
bean at runtime. In the end, you write no lookup code and can easily change configuration to swap out beans and resources as needed. In essence, DI allows you to declare component dependencies and lets the container deal with the complexities of service or resource instantiation, initialization, sequencing, and supplies the service or resource references to the clients as required. As we work our way through the examples in this chapter, you ll see several places where we use DI, including @EJB to inject EJBs in section 2.3, @Resource to inject JMS resources in section 2.4, and @PersistenceContext to inject container-managed EntityManager in section 2.5.
NOTE
Lightweight application containers like the Spring Framework and PicoContainer popularized the idea of DI. To learn more about the roots of DI itself, visit www.martinfowler.com/articles/injection.html. This article, by Martin Fowler, faithfully examines the pros and cons of DI over JNDIstyle manual lookups. Since the article was written before EJB 3 was conceived, you might find the discussion of EJB 2 cool as well!
Now that we ve covered some of the most fundamental concepts of EJB 3, it is time to warm up to code. The problem we solve in this chapter utilizes an essential element of this book ActionBazaar. ActionBazaar is an imaginary enterprise system around which we ll weave most of the material in this book. In a sense, this book is a case study of developing the ActionBazaar application using EJB 3. Let s take a quick stroll around the bazaar to see what it is all about.
Copyright © OnBarcode.com . All rights reserved.