Web Hosting SSH - Mastering Enterprise J2EE

14 Chapter 1 Access another system. Examples include calling a high-performing CICS legacy system written in COBOL that computes the risk factor for a new insurance account, calling a legacy VSAM data store, or calling SAP R/3. Enterprise beans can integrate with an existing application through the J2EE Connector Architecture (JCA), which we will talk about in detail in Chapter 17. Thus, EJB components are not presentation tier components; rather, they sit behind the presentation tier components (or clients) and do all the hard work. Examples of the clients that can connect to enterprise beans include the following: Thick clients. Thick clients execute on a user s desktop. They could connect through the network with EJB components that live on a server. These EJB components may perform any of the tasks listed previously (business logic, database logic, or accessing other systems). Thick clients in Java include applets and applications. Dynamically generated Web pages. Web sites that are transactional and personalized in nature need their Web pages generated specifically for each request. For example, the home page for Amazon.com is completely different for each user, depending on the user s profile. Core technologies such as Java servlets and JavaServer Pages (JSP) are used to dynamically generate such specific pages. Both servlets and JSPs live within a Web server and can connect to EJB components, generating pages differently based upon the values returned from the EJB layer. Web Service clients. Some business applications require no user interface at all. They exist to interconnect with other business partners applications that may provide their own user interface. For example, consider a scenario where Dell Computer Corporation needs to procure Intel chips to assemble and distribute desktop computers. Here, Intel could expose an Order Parts Web Service that enables the Dell Web Service client to order chips. In this case, the Intel system does not provide a graphical user interface per se, but rather provides a Web Service interface. This scenario is shown in Figure 1.4.
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