SWE 316: Software Design and Architecture Objectives Lecture # 19 Java Beans SWE 316: Software Design and Architecture Understand what JavaBeans (“Beans”)

SWE 316: Software Design and Architecture

Obj

ecti

ves

Lecture # 19

Java Beans


Understand what JavaBeans

(“Beans”) are?

the life-cycle of a Bean

Bean containers

Be able to create JavaBeans

connect Beans in BeanBox

create applications that use Beans

Ch 11Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.


Java Beans Design Goals 1

Create a component technology within Java capitalize on Java portability

Include GUI components but not limited to GUI (e.g. server bean)

Compete with other visual programming and component systems (which are often specific to an O.S.)

usually Windows

require installation of some kind

IntroCreating Bean

ClassesMultiple-Class

BeansDeploying

BeansConnecting

BeansBeans in JSP 2/29


Beans Design Goals 2 “Light weight” for Internet applications Secure

use Java security model Easy & efficient to distribute Provide mechanism which enables

development environment (“container”) to determine methods, properties & events

Facilitate the easy reuse of Java code.

KEY CONCEPTDesign Goal: Reusability

IntroCreating Bean


BeansDeploying

BeansConnecting



Phase 1. Create Bean Classes

Source subject to rules

Phase 3. Create Bean Instance

Instantiate object(s), usually in a Bean environment (container)

Phase 4a. Combine Beans in Bean Container to Make Application

Combine with other Beans to produce application

Bean Phases

Phase 2. Create Bean from Multiple Bean Classes

Combine Bean classes to make new Beans; create manifest; compile

Phase 4b. Deploy Bean and Use in Applications

Place application, Beans and required software on target platform

- or -

Design / implementation time.

Instance creation time.

Assembly time.

Deployment time.

--------

IntroCreating Bean


BeansDeploying

BeansConnecting



Amenities Afforded by Bean Environments

Detection of the Bean’s propertiesRead only – or-

Writeable

Detection of listeners supportedSo events on the Bean can be handled

Ability to easily create instancesand display an image if an awt or swing object

Set property values visually

Ability to store instances

IntroCreating Bean


BeansDeploying

BeansConnecting



Required Bean Rules 1 of 2 Java source consists of Java classes

containing null constructor … MyClass() { … }

implementing Serializable interface

obeying standards shown below for …… accessor methods … Listener registration … Event classes

IntroCreating Bean


BeansDeploying

BeansConnecting



Required Bean Rules 2 of 2 To have property myProp, include methods:

<type> getMyProp(){ … } // to access myProp

void setMyProp( <type> p ) // to change

For boolean property:

boolean isMyProp() Name for event classes to be XXXEvent

extends Event

Listeners must implement java.util.EventListener Name must end in Listener as in XXXListener added with public void addXXXListener(...) removed with public void removeXXXListener(...)

IntroCreating Bean


BeansDeploying

BeansConnecting



Phase 1: creating bean classes (cont...)

Compile the bean:javac Bean0.java

Create manifest (text file): specifies the name of the class file comprising the bean and indicates that they are indeed JavaBeans (other required files can also be included). The manifest file becomes part of the JAR fileName: Bean0.classJava-Bean: True

11.3

Intro Creating Bean Classes

Multiple-Class Beans

Deploying Beans

Connecting Beans

Beans in JSP 8/29


Bean0 source codepublic class Bean0

implements java.io.Serializable // required for Beans

{

private int myInt = 0; // ("myInt" is not necessarily a property yet!)

public Bean0() // Null constructor presence required for all Beans

{

}

public int getIntgr() // Introduces property "intgr" and makes gettable

{ return myInt;

}

public void setIntgr( int anInteger ) // Makes property "intgr" settable

{ myInt = anInteger;

}

}



Deploying Beans

Connecting Beans

Beans in JSP 9/29


JAR’ing a Beanjar cfm Bean0.jar manifest.txt Bean0.class

Creating a JAR file

First argument is name of the new JAR file

Second argument is name of manifest file

List all .class files to be included



Deploying Beans

Connecting Beans

Beans in JSP 10/29


BeanBox Environment



Deploying Beans

Connecting Beans

Beans in JSP 11/29


Adding a Bean to the BeanBox



Deploying Beans

Connecting Beans

Beans in JSP 12/29


Bean1



Deploying Beans

Connecting Beans

Beans in JSP 13/29


Bean1 source codeimport java.awt.*;

public class Bean1 extends Canvas implements java.io.Serializable

{private Color color = Color.red; // color of

interior rectangle

// Set background (color) and size// propertiespublic Bean1() { setBackground( Color.green );

setSize( 80,40 );}

// Establish property "color"public Color getColor() { return color;}

public void setColor( Color aColor ) { color = aColor;}

// Override paint: rectangle and // message within this Canvas object// Called initially and when developer // changes a property in BeanBoxpublic void paint ( Graphics g ) {

// Draw rectangle in "color"g.setColor( color );// Starting from top left within // this: 20 pixels across, 5 down// draw a filled rectangle 20 // across and 30 downg.fillRect( 30,5,20,30 );

// Write "HELLO WORLD" in the // foreground colorg.setColor( getForeground() );g.drawString( "HELLO WORLD", 5, 20 );

}}



Deploying Beans

Connecting Beans

Beans in JSP 14/29


Setting Color



Deploying Beans

Connecting Beans

Beans in JSP 15/29


Phase 2: creating multiple-class beans

initial Form of Properties Panel

To create a bean consisting of more than one class: Create these classes in conformance with Bean

rules Declare them in the manifest file Jar them all E.g.:

jar cfm MyBean.jar manifestListingAll.txt MyBean1.class MyBean2.class … MyBeanN.class

11.4

IntroCreating Bean


BeansDeploying

BeansConnecting



Phase 3: creating bean instance BeanBox helps

the user to create instances of Bean classes by allowing the user to set some properties visually.

(green in color)

11.5

IntroCreating Bean


BeansDeploying

BeansConnecting



Phase 4: combining and deploying beans Phase 4a: combining Beans in Bean

environment Beginning to Use ChairMaker

IntroCreating Bean


BeansDeploying

BeansConnecting




environment Setting ChairMaker to Add a Chair Leg

IntroCreating Bean


BeansDeploying

BeansConnecting




environment, An Output Of ChairMaker Bean

IntroCreating Bean


BeansDeploying

BeansConnecting




environment Output Of ChairMaker Bean From Button Action

IntroCreating Bean


BeansDeploying

BeansConnecting



Phase 4: combining and deploying beans Phase 4b: using Beans in applications: Output

Object bean1 = Beans.instantiate(null, “Bean1”); Bean1 bean2 = (Bean1)objectInputStream.readObject();

We want to associate Beans even when there is no external event such as a mouse click.

KEY CONCEPTReusability

IntroCreating Bean


BeansDeploying

BeansConnecting



Connecting Beans via property changes: “bound” variables

Property Change Event Demonstration

11.7

IntroCreating Bean


BeansDeploying

BeansConnecting



Connecting Beans via property changes: “bound” variables

Property Change Event Demonstration (cont...)

IntroCreating Bean


BeansDeploying

BeansConnecting



Connecting beans via property changes: “bound” variables

bound property demonstration

-- causes a Beans to react when a property in another Bean changes value.

KEY CONCEPTBound Properties

IntroCreating Bean


BeansDeploying

BeansConnecting



Embedding Beans in JSP<jsp:useBean

id="object name" 1scope="page|request|session|application" 2class="fully qualified classname" 3

</ jsp:useBean >

1 Bean instance name as in MyClass myName = ….

2 // Choose one; when instance is destroyed; optional; default is page

3 // e.g., a.b.MyClass

11.8

IntroCreating Bean


BeansDeploying

BeansConnecting

Beans Beans in JSP 26/29


Scope of a Bean in a JSP page - new object created and destroyed for

every page view. request - the newly created object created and

bound to the request object. session - the newly created object bound to the

session object. -- every visitor coming to the site will have a separate session for it, so you will not have to create a new object every time for it -- can retrieve that object later again from the session object when wanted

application - object will stay as long as the application remains loaded. E.g., you want to count page views or daily sessions for your site. Source: http://stardeveloper.com:8080/articles/072001-1.shtml

IntroCreating Bean


BeansDeploying

BeansConnecting



Setting and Getting a Bean Property in a JSP: Introduction

<jsp:setProperty name=“account17" property=“bal" value=“3211“ />

<jsp:getProperty name=“account17" property=“bal" />

IntroCreating Bean


BeansDeploying

BeansConnecting



Summary of This Chapter A Java Bean is a compiled collection of Java

classes and required files JAR’d to reduce to a single file

Beans are used at various phases, often in a Bean container Creating from scratch Creating instances of Connecting Deploying as part of an application

IntroCreating Bean


BeansDeploying

BeansConnecting


Documents

SWE 316: Software Design and Architecture Objectives Lecture # 19 Java Beans SWE 316: Software Design and Architecture Understand what JavaBeans (“Beans”)