Head First EJB

What is EJB all about?

Component-based development

With enterprise javabeans, you can develop building blocks—EJB components—that you or someone else can assemble and reassemble into different applications. For example, you might create a Customer bean (bean is another word for component) that represents a customer in a database. You can use that Customer bean in an accounting program, an e-commerce shopping cart system, a tech support application, or virtually any other application that might need to represent a customer. In fact, with some beans, the bean developer and the application assembler might not work for the same company or have any knowledge of one another.

If you’re a bean developer, you might build an Order bean, or a Payroll bean, or a ShoppingCart bean that developers in some unrelated company can buy and use to construct their own custom applications.

One beauty of component-based development is that you take code reuse to a whole new level. Instead of reusing Java classes, you get to reuse a bigger chunk of functionality. Often, you can modify the way a bean works without ever touching its Java code! You’ll learn in this chapter that when you deploy a bean into a server, you can configure and customize the bean declaratively—through an XML-based deployment descriptor—to change the way the bean behaves at runtime.

With component-based development, you take code reuse to a whole new level. With OO development, you reuse classes, but with components, you reuse a bigger chunk of functionality, and you can customize them without touching code!

Application A: online shopping

Fred assembles an online shopping application using two components he bought from Beans-R-Us, plus a third component Fred developed at his company.

Application B: technical support

Bill assembles a technical support app using two components he bought from Beans-R-Us, plus two components he developed himself.