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The Java EE 5 Tutorial (PDF) - Oracle Software Downloads

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FIGURE 1–1 Multitiered Applications<br />

■ Enterprise information system (EIS)-tier software runs on the EIS server.<br />

Although a <strong>Java</strong> <strong>EE</strong> application can consist of the three or four tiers shown in Figure 1–1, <strong>Java</strong><br />

<strong>EE</strong> multitiered applications are generally considered to be three-tiered applications because<br />

they are distributed over three locations: client machines, the <strong>Java</strong> <strong>EE</strong> server machine, and the<br />

database or legacy machines at the back end. Three-tiered applications that run in this way<br />

extend the standard two-tiered client and server model by placing a multithreaded application<br />

server between the client application and back-end storage.<br />

<strong>Java</strong> <strong>EE</strong> Application 1 <strong>Java</strong> <strong>EE</strong> Application 2<br />

Application<br />

Client<br />

Enterprise Beans<br />

Security<br />

Dynamic<br />

HTML Pages<br />

JSP Pages<br />

Enterprise Beans<br />

Database Database<br />

Client Tier<br />

Web Tier<br />

Business Tier<br />

EIS Tier<br />

Distributed Multitiered Applications<br />

Client<br />

Machine<br />

<strong>Java</strong> <strong>EE</strong><br />

Server<br />

Database<br />

Server<br />

While other enterprise application models require platform-specific security measures in each<br />

application, the <strong>Java</strong> <strong>EE</strong> security environment enables security constraints to be defined at<br />

deployment time. <strong>The</strong> <strong>Java</strong> <strong>EE</strong> platform makes applications portable to a wide variety of<br />

security implementations by shielding application developers from the complexity of<br />

implementing security features.<br />

Chapter 1 • Overview 41

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