Transcript JavaBeans n
JavaBeans A component architecture 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 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 platformindependent 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 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 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 Events A mechanism for propagating state change notifications between a source object and one or more target listener objects 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. 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 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.Label=foo”) by programming through getter and setter methods in a property sheet for a user to edit when a component is customized Typically a bean’s properties will be persistent 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 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) 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 Manually -- Using beans in a handwritten 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 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.general.html 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.general.html 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, K&A 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.general.html 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 fullfledged Java desktop applications to web-based Applets. * source: http://java.sun.com/beans/faq/faq.general.html 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.general.html