Lesson: JavaBeans Concepts
By dananourie on Feb 01, 2008
The JavaBeans™ architecture is based on a component model which enables developers to create software units called components. Components are self-contained, reusable software units that can be visually assembled into composite components, applets, applications, and servlets using visual application builder tools. JavaBean components are known as beans.
A set of APIs describes a component model for a particular language. The
specification describes the core detailed elaboration for the JavaBeans
Beans are dynamic in that they can be changed or customized. Through the design mode of a builder tool you can use the Properties window of the bean to customize the bean and then save (persist) your beans using visual manipulation. You can select a bean from the toolbox, drop it into a form, modify its appearance and behavior, define its interaction with other beans, and combine it and other beans into an applet, application, or a new bean.
The following list briefly describes key bean concepts.
- Builder tools discover a bean's features (that is, its properties,
methods, and events) by a process known as
Beans support introspection in two ways:
- By adhering to specific rules,
known as design patterns, when
naming bean features. The
Introspectorclass examines beans for these design patterns to discover bean features. The
Introspectorclass relies on the core reflection API. The trail The Reflection API is an excellent place to learn about reflection.
- By explicitly providing property, method, and event information with
a related bean
information class. A bean information
class implements the
BeanInfoclass explicitly lists those bean features that are to be exposed to application builder tools.
- By adhering to specific rules, known as design patterns, when naming bean features. The
- Properties are the appearance and behavior characteristics of a bean that can
be changed at design time. Builder tools introspect on a bean to discover its
properties and expose those properties for manipulation.
- Beans expose properties so they can be customized
at design time.
Customization is supported in two ways: by using property editors, or by using
more sophisticated bean customizers.
- Beans use events to communicate with other beans. A bean that is to
receive events (a listener bean) registers with the bean that fires the event (a
source bean). Builder tools can examine a bean and determine which events that
bean can fire (send) and which it can handle (receive).
- Persistence enables beans to save and restore their state. After changing
a bean's properties, you can save the state of the bean and restore that bean at
a later time with the property changes intact. The JavaBeans architecture uses
Java Object Serialization to support persistence.
- A bean's methods are no different from Java methods, and can be called from other beans or a scripting environment. By default all public methods are exported.
Beans vary in functionality and purpose. You have probably met some of the following beans in your programming practice:
- GUI (graphical user interface)
- Non-visual beans, such as a spelling checker
- Animation applet
- Spreadsheet application
Read more from the JavaBeans Trail