birt barcode tool Part 2 Building business logic with EJB 3 in Java

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Part 2 Building business logic with EJB 3
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art 2 of this book covers how you can use EJB 3 components (session beans and message-driven beans) to build business logic for your enterprise Java applications. 3 covers session beans in detail and describes the development of both stateless and stateful beans and their clients. The chapter provides guidelines to help you decide whether to use stateless or stateful session beans. Asynchronous communication is accomplished by messaging, and chapter 4 explores messaging and message-driven beans. You can use several advanced features, such as dependency injection, interceptors, and timers; these topics are examined in chapter 5. 6 covers enterprise applications development concerns, such as transaction and security.
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Building business logic with session beans
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This chapter covers
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Development of stateless and stateful session beans Session bean lifecycle Session bean clients Session bean performance considerations and best practices
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Building business logic with session beans
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At the heart of any enterprise application lies its business logic. In an ideal world, application developers should only be concerned with defining and implementing the business logic, while concerns like presentation, persistence, or integration should largely be window dressing. From this perspective, session beans are the most important part of the EJB technology because their purpose in life is to model high-level business processes. If you think of a business system as a horse-drawn chariot with a driver carrying the Greco-Roman champion to battle, session beans are the driver. Session beans utilize data and system resources (the chariot and the horses) to implement the goals of the user (the champion) using business logic (the skills and judgment of the driver). For this and other reasons, sessions beans, particularly stateless session beans, have been popular, even despite the problems of EJB 2. EJB 3 makes this vital bean type a lot easier to use. In chapter 1 we briefly introduced session beans. In chapter 2 we saw simple examples of these beans in action. In this chapter, we ll discuss session beans in much greater detail, focusing on their purpose, the different types of session beans, how to develop them, and some of the advanced session bean features available to you. We start this chapter by exploring some basic session bean concepts, and then discuss some fundamental characteristics of session beans. We then cover each type stateful and stateless in detail before introducing bean client code. Finally, we examine session bean best practices at the end of the chapter.
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3.1 Getting to know session beans
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A typical enterprise application will have numerous business activities or processes. For example, our ActionBazaar application has processes such as creating a user, adding an item for auctioning, bidding for an item, ordering an item, and many more. Session beans can be used to encapsulate the business logic for all such processes. The theory behind session beans centers on the idea that each request by a client to complete a distinct business process is completed in a session. So what is a session If you have used a Unix server you may have used Telnet to connect to the server from a PC client. Telnet allows you to establish a login session with the Unix server for a finite amount of time. During this session you may execute several commands in the server. Simply put, a session is a connection between a client and a server that lasts for a finite period of time.
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Getting to know session beans
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A session may either be very short-lived, like an HTTP request, or span a long time, like a login session when you Telnet or FTP into a Unix server. Similar to a typical Telnet session, a bean may maintain its state between calls, in which case it is stateful, or it may be a one-time call, in which case it s stateless. A typical example of a stateful application is the module that a bidder uses to register himself in the ActionBazaar application. That process takes place in multiple steps. An example of a stateless business module is the application code that is used to place a bid for an item. Information, such as user ID, item number, and amount, is passed in and success or failure is returned. This happens all in one step. We ll examine the differences between stateless and stateful session beans more closely in section 3.1.4. As you might recall, session beans are the only EJB components that are invoked directly by clients. A client can be anything, such as a web application component (servlet, JSP, JSF, and so on), a command-line application, or a Swing GUI desktop application. A client can even be a Microsoft .NET application using web services access. At this point you might be wondering what makes session beans special. After all, why use a session bean simply to act as a business logic holder Glad that you asked. Before you invest more of your time, let s address this question first. Then we ll show you the basic anatomy of a session bean and explore the rules that govern it before examining the differences between stateless and stateful session beans.
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