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barcode font vb.net EJB as a component in Java
1.1.1 EJB as a component Creating Data Matrix ECC200 In Java Using Barcode generation for Java Control to generate, create ECC200 image in Java applications. www.OnBarcode.comScanning Data Matrix ECC200 In Java Using Barcode decoder for Java Control to read, scan read, scan image in Java applications. www.OnBarcode.comIn this book, when we talk about EJBs, we are referring to the server-side components that you can use to build parts of your application, such as the business logic or persistence code. Many of us tend to associate the term component with developing complex and heavyweight CORBA, Microsoft COM+ code. In the brave new world of EJB 3, a component is what it ought to be nothing more than a POJO with some special powers. More importantly, these powers remain invisible until they are needed and don t distract from the real purpose of the component. You will see this firsthand throughout this book, especially starting with chapter 2. The real idea behind a component is that it should effectively encapsulate application behavior. The users of a component aren t required to know its inner workings. All they need to know is what to pass in and what to expect back. Data Matrix 2d Barcode Drawer In Java Using Barcode encoder for Java Control to generate, create DataMatrix image in Java applications. www.OnBarcode.comCode 128 Drawer In Java Using Barcode printer for Java Control to generate, create Code 128A image in Java applications. www.OnBarcode.comWhat s what in EJB 3
Creating UPC - 13 In Java Using Barcode printer for Java Control to generate, create UPC - 13 image in Java applications. www.OnBarcode.comPaint UCC.EAN - 128 In Java Using Barcode generation for Java Control to generate, create GTIN - 128 image in Java applications. www.OnBarcode.comThere are three types of EJB components: session beans, message-driven beans, and entities. Session beans and message-driven beans are used to implement business logic in an EJB application, and entities are used for persistence. Components can be reusable. For instance, suppose you re in charge of building a website for an online merchant that sells technology books. You implement a module to charge the credit card as part of a regular Java object. Your company does fairly well, and you move on to greener pastures. The company then decides to diversify and begins developing a website for selling CDs and DVDs. Since the deployment environment for the new site is different, it can t be located on the same server as your module. The person building the new site is forced to duplicate your credit card module in the new website because there s no easy way to access your module. If you had instead implemented the credit card charging module as an EJB component as shown in figure 1.1 (or as a web service), it would have been much easier for the new person to access it by simply making a call to it when she needed that functionality. She could have reused it without having to understand its implementation. Given that, building a reusable component requires careful planning because, across enterprise applications within an organization, very little of the business logic may be reusable. Therefore, you may not care about the reusability of EJB components, but EJB still has much to offer as a framework, as you ll discover in the next section. Making UPC-A Supplement 5 In Java Using Barcode creation for Java Control to generate, create UCC - 12 image in Java applications. www.OnBarcode.comPrint Identcode In Java Using Barcode printer for Java Control to generate, create Identcode image in Java applications. www.OnBarcode.comFigure 1.1 EJB allows development of reusable components. For example, you can implement the credit card charging module as an EJB component that may be accessed by multiple applications. Data Matrix 2d Barcode Generator In Objective-C Using Barcode drawer for iPhone Control to generate, create ECC200 image in iPhone applications. www.OnBarcode.comData Matrix ECC200 Creator In None Using Barcode creation for Word Control to generate, create Data Matrix 2d barcode image in Word applications. www.OnBarcode.comEJB overview
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GS1 - 13 Generation In Visual Studio .NET Using Barcode generation for ASP.NET Control to generate, create GTIN - 13 image in ASP.NET applications. www.OnBarcode.comScan QR In Java Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications. www.OnBarcode.comAs we mentioned, EJB components live in a container. Together, the components, or EJBs, and the container can be viewed as a framework that provides valuable services for enterprise application development. Although many people think EJBs are overkill for developing relatively simple web applications of moderate size, nothing could be further from the truth. When you build a house, you don t build everything from scratch. Instead, you buy materials or even the services of a contractor as you need it. It isn t too practical to build an enterprise application from scratch either. Most server-side applications have a lot in common, including churning business logic, managing application state, storing and retrieving information from a relational database, managing transactions, implementing security, performing asynchronous processing, integrating systems, and so on. As a framework, the EJB container provides these kinds of common functionality as out-of-the-box services so that your EJB components can use them in your applications without reinventing the wheel. For instance, let s say that when you built the credit card module in your web application, you wrote a lot of complex and error-prone code to manage transactions and security access control. You could have avoided that by using the declarative transaction and security services provided by the EJB container. These services, as well as many others you ll learn about in section 1.3, are available to the EJB components when they are deployed in the EJB container, as you can see in figure 1.2. This means writing high-quality, feature-rich applications much faster than you might think. The container provides the services to the EJB components in a rather elegant new way: metadata annotations are used to preconfigure the EJBs by specifying the type of services to add when the container deploys the EJBs. Java 5 introduced Barcode Generation In Objective-C Using Barcode drawer for iPhone Control to generate, create Barcode image in iPhone applications. www.OnBarcode.comDecode DataMatrix In None Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications. www.OnBarcode.comDrawing Code 128 Code Set C In Java Using Barcode printer for Android Control to generate, create USS Code 128 image in Android applications. www.OnBarcode.comDraw Barcode In .NET Framework Using Barcode encoder for VS .NET Control to generate, create Barcode image in Visual Studio .NET applications. www.OnBarcode.comCode 39 Printer In Visual Studio .NET Using Barcode creator for .NET Control to generate, create Code 3 of 9 image in VS .NET applications. www.OnBarcode.comGenerate EAN / UCC - 13 In .NET Framework Using Barcode creation for ASP.NET Control to generate, create GS1-128 image in ASP.NET applications. www.OnBarcode.com |
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