JavaBeans

1
JavaBeans

• A component architecture

2
What is JavaBeans?

• NC World (New Computing) Dictionary
• JavaBeans n. 1. JavaSoft technology. 2. Component
  object model for creating modular applications
  (see object computing)
• object computing n. 1. A system delivers modular
  programming to the computing mainstream (see
  Java)
• Java n. 1. A type of object computing system that
  allow you to create a variety of objects
• The dream of JavaBeans is ..
• Development of software by building blocks
  through drag drop

3
What is JavaBeans?

• A Java Bean is a reusable software component that
  can be manipulated visually in a builder tool
• JavaBeans is a portable, platform-independent
  component model written in the Java programming
  language, developed in collaboration with
  industry leaders.
• It enables developers to write reusable
  components once and run them anywhere --
  benefiting from the platform-independent power of
  Java technology.
• The goal of JavaBeans is to create a system
  whereby application developers can take a set of
  beans from a stock library and wire them together
  to make a full application

4
Features of JavaBeans

• Support for introspection
• so that a builder tool can analyze how a bean
  works
• Support for customization
• so that when using an application builder a user
  can customize the appearance and behavior of a
  bean
• Support for events
• as a simple communication metaphor than can be
  used to connect up beans
• Support for properties
• both for customization and for programmatic use
• Support for persistence
• so that a bean can be customized in an
  application builder and then have its customized
  state saved away and reloaded later

5
Persistent Storage

• Purpose
• To use existing data formats and plug into OLE or
  OpenDoc documents (e.g., Excel doc inside a Word
  doc)
• To be trivial for the common case of a tiny
  Bean (by saving its internal state)
• Solutions
• Externalization provides a Bean with full
  control over the resulting data layout.
• Serialization provides an automatic way of
  storing out and restoring the internal state of a
  collection of Java objects
• All bean must support either Serialization or
  Externalization

6
Events

• A mechanism for propagating state change
  notifications between a source object and one or
  more target listener objects

7
Event Adaptors

• Motivation When additional behavior is required
  during event delivery, an intermediary event
  adaptor class may be defined, and interposed
  between an event source and the real event
  listener.

8
Examples of Event Adaptors

• Implementing an event queuing mechanism between
  sources and listeners
• Acting as a filter
• Demultiplexing multiple event sources onto a
  single event listener
• Acting as a generic wiring manager between
  sources and listeners

9
Properties

• Discrete, named attributes of a Java Bean
• that can affect its appearance or its behavior
• E.g., label in a GUI button to represent the
  displayed text
• Properties show up in a number of ways
• through scripting environments (like object
  fields, e.g., b.Labelfoo)
• by programming through getter and setter methods
• in a property sheet for a user to edit when a
  component is customized
• Typically a beans properties will be persistent

10
Introspection

• A process of understanding which properties,
  events, and methods a Java Bean supports at
  runtime and in their builder environment
• Purpose to avoid using any separate
  specification language for defining the behavior
  of a Java Bean.
• All of its behavior would be specifiable in Java
• Solution Approaches
• Reflection a low level mechanism to study the
  methods supported by a target bean
• Design patterns to deduce from those methods
  what properties, events, and public methods are
  supported

11
Customization

• Ability to customize the appearance and behavior
  of the various beans they are using when a user
  is composing an application in an application
  builder
• Two ways
• An application builder through GUI property sheet
  ( property list property editor)
• Wizards that guide users through the different
  steps of customizing a bean (for larger or
  complex beans)

12
Automated -- Using an application builder to
construct an Applet

• 1. Buying the tools
• 2. Laying out the applet
• create a new applet and drag-and-drop beans in
  the application builder
• 3. Customizing the beans
• Select the button and edit the properties using
  the application builder
• 4. Connecting up the beans
• 5. Packaging up the applet
• 6. Trying it out

13
Manually -- Using beans in a hand-written Applet

• 1. Loading the tools
• 2. Laying out the applet
• - start to type in the code for a new applet
  (init method)
• 3. Customizing the beans
• - through calling on the beans property
  accessor methods (e.g., btn.setBackground(java.awt
  .Color.red))
• 4. Connecting up the beans
• 5. Packaging up the applet
• 6. Trying it out

14
FAQ 1

• Why are component architectures useful?
• Developers are turning to creating components
  rather than monolithic applications to free
  themselves from slow, expensive application
  development, and to build up a portable, reusable
  code base. This enables developers to quickly
  attack new market opportunities, new joint
  development opportunities, and new ways to sell
  smaller packages of software.

source http//java.sun.com/beans/faq/faq.genera
l.html
15
FAQ 2

• Is JavaBeans a complete component architecture?
• JavaBeans is a complete component model. It
  supports the standard component architecture
  features of properties, events, methods, and
  persistence. In addition, JavaBeans provides
  support for introspection (to allow automatic
  analysis of a JavaBeans component) and
  customization (to make it easy to configure a
  JavaBeans component).

source http//java.sun.com/beans/faq/faq.genera
l.html
16
FAQ 3

• Are there JavaBeans components available that I
  can buy today?
• Yes. A large number of companies, both large and
  small, have announced their plans to deliver
  JavaBeans-based products including Corel,
  EnterpriseSoft, Gemstone, IBM, JScape, KA
  Software, KL Group, Lotus Development, Novell,
  ProtoView Development, Rogue Wave, and Stingray
  Software among many others. Contact these
  companies for information on product
  availability. Many more companies have adopted
  the JavaBeans component model, take a look at the
  JavaBeans Directory.

source http//java.sun.com/beans/faq/faq.genera
l.html
17
FAQ 4

• What are the security implications for
  downloading Beans over the Internet?
• JavaBeans does not add any security features to
  the Java platform. Rather, JavaBeans components
  have full access to the broad range of security
  features that are part of the Java platform.
  JavaBeans components can be used to build a range
  of different kinds of solutions from full-fledged
  Java desktop applications to web-based Applets.

source http//java.sun.com/beans/faq/faq.genera
l.html
18
FAQ 5

• Does the 100 Pure Java program ensure
  compatibility and interoperability between Beans?
  
• The 100 Pure Java Initiative is a program
  designed specifically for developers of Java
  software. Sun will provide testing and marketing
  support specifically for JavaBeans components in
  the first half of 1998.

source http//java.sun.com/beans/faq/faq.genera
l.html