Component-Based Component-Based Software EngineeringSoftware Engineering

Introduction to Java BeansIntroduction to Java Beans

Paul KrausePaul Krause

andand

Sotiris MoschoyiannisSotiris Moschoyiannis

Java BeansJava Beans

ContentsContents

DefinitionDefinition Bean BasicsBean Basics

What is a Java Bean?What is a Java Bean?

““A Java Bean is a reusable software A Java Bean is a reusable software component that can be manipulated component that can be manipulated visually in a builder tool”visually in a builder tool”

JavaSoftJavaSoft

Sources of Builder ToolsSources of Builder Tools

NetBeans:NetBeans:http://www.http://www.netbeansnetbeans.org.org

JBuilder:JBuilder:http://www.http://www.borlandborland.com/.com/jbuilderjbuilder//

Note, you also need to have the Java Note, you also need to have the Java SDK installed.SDK installed.

Bean BooksBean Books

Developing Developing Java BeansJava Beans

Robert Robert EnglanderEnglander

O’ReillyO’Reilly RecommendedRecommended

JavaBeans JavaBeans ProgrammingProgramming

J. O’Neil and J. O’Neil and

H. SchildtH. Schildt

McGraw HillMcGraw Hill Good. Contains Good. Contains many examples.many examples.

JavaBeans by JavaBeans by ExampleExample

Henri JubinHenri Jubin Prentice HallPrentice Hall Simpler than the Simpler than the above, but with above, but with useful examplesuseful examples

NetBeans – the NetBeans – the Definitive GuideDefinitive Guide

Boudreau, Boudreau, Glick, Greene, Glick, Greene, Spurlin, WoehrSpurlin, Woehr

O’ReillyO’Reilly Not so good on Not so good on Beans. More Beans. More about the IDE.about the IDE.

Java BeansJava Beans

ContentsContents

DefinitionDefinition Bean BasicsBean Basics

The Component ModelThe Component Model

JavaBeans is Java’s component modelJavaBeans is Java’s component model The model is made up of an architecture The model is made up of an architecture

and an APIand an API The API makes it possible to write The API makes it possible to write

component software in Javacomponent software in Java The architecture provides the framework The architecture provides the framework

(services and rules) that allows (services and rules) that allows components to participate properlycomponents to participate properly

The Component ModelThe Component Model

Discovery and RegistrationDiscovery and Registration Raising and Handling of EventsRaising and Handling of Events PersistencePersistence Visual PresentationVisual Presentation Support for Visual ProgrammingSupport for Visual Programming

The Component ModelThe Component Model

Discovery and RegistrationDiscovery and Registration

Locate a component at run-time and Locate a component at run-time and determine its supported interfacesdetermine its supported interfaces

Registration process for a component to make Registration process for a component to make itself and its interfaces knownitself and its interfaces known

This mechanism allows components and This mechanism allows components and applications to be developed independentlyapplications to be developed independently

The Component ModelThe Component Model

Raising and Handling of EventsRaising and Handling of Events

Beans (or JavaBeans components) use Beans (or JavaBeans components) use events to communicate with other Beansevents to communicate with other Beans

A Bean that wants to receive events (a A Bean that wants to receive events (a listener listener Bean) registers its interest with the Bean) registers its interest with the Bean that triggers the event (a Bean that triggers the event (a sourcesource Bean) Bean)

The Component ModelThe Component Model

PersistencePersistence

Persistence enables Beans to save and Persistence enables Beans to save and restore their staterestore their state

JavaBeans uses Java Object Serialization to JavaBeans uses Java Object Serialization to support persistence support persistence

The Component ModelThe Component Model

Visual PresentationVisual Presentation

The Bean is free to choose its own visual The Bean is free to choose its own visual presentation (fonts, colours, shape, etc)presentation (fonts, colours, shape, etc)

Many of these characteristics will be Many of these characteristics will be properties of the Bean (some might be properties of the Bean (some might be persistent too)persistent too)

The Component ModelThe Component Model

Support of Visual ProgrammingSupport of Visual Programming

User can select a component from the User can select a component from the toolbox and place it into a containertoolbox and place it into a container

Properties of the component can then be Properties of the component can then be edited to create the desired behaviouredited to create the desired behaviour

Bean’s PropertiesBean’s Properties

Properties are a Bean’s appearance and Properties are a Bean’s appearance and behaviour characteristics that can be behaviour characteristics that can be changed at design timechanged at design time

By following specific naming conventions, By following specific naming conventions, the properties of a Bean that are the properties of a Bean that are “revealed” to the world can be identified“revealed” to the world can be identified

Conventions for Access Conventions for Access MethodsMethods

Simple Properties:Simple Properties: For a property of type For a property of type TypeType and name and name Name:Name: public public TypeType get getNameName( );( ); public void setpublic void setNameName((TypeType valuevalue););

Boolean Properties:Boolean Properties: public boolean ispublic boolean isNameName( );( ); public void setpublic void setNameName(boolean (boolean valuevalue););

Bean MethodsBean Methods

A Bean may be implemented by a Java A Bean may be implemented by a Java ClassClass

That Class contains a number of methods That Class contains a number of methods that may be used to access and control that may be used to access and control the Beanthe Bean

These are generally all the public methods These are generally all the public methods of the Class that implements the Beanof the Class that implements the Bean

EventsEvents

JavaBeans components interact by JavaBeans components interact by generating “Events”generating “Events”

Several components may register an Several components may register an interest in an Event that is generated by a interest in an Event that is generated by a specific componentspecific component

Occurrence of the Event triggers methods Occurrence of the Event triggers methods to be called in all the components that are to be called in all the components that are “listening” for it“listening” for it

IntrospectionIntrospection

The process by which builder tools The process by which builder tools discover a Bean’s featuresdiscover a Bean’s features

Beans support introspection in two ways:Beans support introspection in two ways: By adhering to specific rules (By adhering to specific rules (design patternsdesign patterns) )

when naming properties, methods and eventswhen naming properties, methods and events By explicitly providing property, method and By explicitly providing property, method and

event info within a event info within a Bean InformationBean Information class class

IntrospectionIntrospection

Low-level reflection:Low-level reflection: Follow Bean coding style (we have seen)Follow Bean coding style (we have seen) Analysis of the Bean’s class can then reveal Analysis of the Bean’s class can then reveal

properties and methodsproperties and methods Revealing complex properties:Revealing complex properties:

Implement a “BeanInfo” classImplement a “BeanInfo” class

CustomisationCustomisation

Beans expose properties so they can be Beans expose properties so they can be customised at design timecustomised at design time

Customisation is supported in two ways:Customisation is supported in two ways: By using property editorsBy using property editors By creating more sophisticated Bean By creating more sophisticated Bean

customiserscustomisers

CustomisationCustomisation

Simple propertiesSimple properties Development tool will build property sheets Development tool will build property sheets

dynamicallydynamically User may then edit the properties to User may then edit the properties to

customise the Beancustomise the Bean For the Advanced UserFor the Advanced User

Create a specific customiser for a BeanCreate a specific customiser for a Bean This is kept separate to the Bean Class, as This is kept separate to the Bean Class, as

with a BeanInfo Classwith a BeanInfo Class

Further FeaturesFurther Features

VisibilityVisibility

It is not necessary for a Bean to be visible at It is not necessary for a Bean to be visible at run-time (e.g. Bean controlling access to a run-time (e.g. Bean controlling access to a device or data feed)device or data feed)

It is necessary however for a Bean to support It is necessary however for a Bean to support the visual builder tool. Even an ‘invisible’ run-the visual builder tool. Even an ‘invisible’ run-time Bean shall be shown on the builder tooltime Bean shall be shown on the builder tool

Further FeaturesFurther Features

MultithreadingMultithreading

Always assume your code will be used in a Always assume your code will be used in a multithreaded environmentmultithreaded environment

Make sure that your Beans are thread-safeMake sure that your Beans are thread-safe Multithreading in JavaBeans is no different Multithreading in JavaBeans is no different

than multithreading in Javathan multithreading in Java

Further FeaturesFurther Features

SecuritySecurity

By default assume that your Beans are By default assume that your Beans are running in a non-trusted appletrunning in a non-trusted applet

Apply security restrictions such asApply security restrictions such as• Allow no access to the local file systemAllow no access to the local file system• Limit socket connections to the host systemLimit socket connections to the host system

SummarySummary

Beans build on Java features that already Beans build on Java features that already existexist

We add a Builder ToolWe add a Builder Tool We use design patternsWe use design patterns We record information about the Classes We record information about the Classes

that implement Beansthat implement Beans