JavaServer Pages, 3rd Edition

Beans as JSP Components

JavaBeans components, or beans for short, are simply regular Java classes designed according to a set of guidelines. By following these guidelines, development tools can figure out how you intend the bean to be used and how it can be linked to other beans. The JavaBeans specification characterizes beans as classes that support:

• Introspection so that a builder tool can analyze how a bean works

• Customization so that, when using an application builder, a user can customize the appearance and behavior of a bean

• Events as a simple communication metaphor than notify beans of interesting things

• Properties, both for customization through a tool and for programmatic use

• Persistence, so that a bean can be customized in an application builder and then have its state saved away and reloaded later

Introspection means that information about a class, such as details about its methods and their parameters and return types, can be discovered by another class. By following certain naming conventions for the methods, the external class can figure out how the bean class is intended to be used. Specifically, the beans properties and the events it generates or observes can be found using the Java Introspection API. For GUI beans, a builder tool uses introspection to discover the bean’s properties and present them to the user in a property window where they can be modified. In a JSP scenario, the JSP standard actions and the EL evaluator use introspection to find the methods for ...