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1.4. Enterprise Computing Scenarios

The previous sections have been rapid-fire introductions to the Java Enterprise APIs. Don't worry if you didn't understand all the information presented there: the rest of the chapters in this Part cover the APIs in more detail. The important message you should take from this chapter is that the Java Enterprise APIs are building blocks that work together to enable you to write distributed Java applications for enterprise computing. The network infrastructure of every enterprise is unique, and the Java Enterprise APIs can be combined in any number of ways to meet the specific needs and goals of a particular enterprise.

Figure 1-1 shows a network schematic for a hypothetical enterprise. It illustrates some of the many possible interconnections among network services and shows the Java Enterprise APIs that facilitate those interconnections. The figure is followed by example scenarios that demonstrate how the Java Enterprise APIs might be used to solve typical enterprise computing problems. You may find it useful to refer to Figure 1-1 while reading through the scenarios, but note that the figure does not illustrate the specific scenarios presented here.

figure

Figure 1-1. The distributed computing architecture of a hypothetical enterprise

1.4.1. Enabling E-Commerce for a Mail-Order Enterprise

CornCo Inc. runs a successful catalog-based mail-order business selling fresh flavored popcorn. They want to expand into the exciting world of electronic commerce over the Internet. Here's how they might do it:[2]

[2]This example is intended to illustrate only how the Java Enterprise APIs can be used together. I have ignored efficiency considerations, so the resulting design might not actually be practical for a large-scale e-commerce web site.

1.4.2. Updating CornCo with Enterprise JavaBeans

You may have noticed a flaw in the previous scenario. The checkout servlet sends billing information to one server, and then sends fulfillment information to another server. But it performs these two actions independently, without any attempt to maintain transactional integrity and make them behave atomically. In other words, if a network failure or server crash were to occur after the billing information had been sent, but before the fulfillment information had been sent, the customer might receive a bill for popcorn that was never shipped.

The designers of the e-commerce system described in the previous section were aware of this problem, but since distributed transactions are complex, and CornCo did not own a transaction management server, they simply chose to ignore it. In practice, the number of customers who would have problems would be small, and it was easier for the original programmers to let the customer service department sort out any irregularities.

But now, CornCo has hired a new Vice President of Information Systems. She's tough as nails, and likes all her i's dotted and her t's crossed. She won't stand for this sloppy state of affairs. As her first official act as VP, she buys a high-end application server with Enterprise JavaBeans support and gives her e-commerce team the job of revamping the online ordering system to use it. The modified design might work like this:



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