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Lecture # 19 Java Beans

SWE 316: Software Design and Architecture. Lecture # 19 Java Beans. Ch 11. 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.

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Lecture # 19 Java Beans

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  1. SWE 316: Software Design and Architecture Lecture # 19Java Beans Ch 11 • 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 Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.

  2. 2/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP 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

  3. 3/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Beans Design Goals 2 KEY CONCEPT Design Goal: Reusability • “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.

  4. 4/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Bean Phases Phase 1. Create Bean Classes Source subject to rules Design / implementation time. Phase 2. Create Bean from Multiple Bean Classes Combine Bean classes to make new Beans; create manifest; compile Instance creation time. Phase 3. Create Bean Instance Instantiate object(s), usually in a Bean environment (container) -------- Assembly time. Phase 4a. Combine Beans in Bean Container to Make Application Combine with other Beans to produce application - or - Deployment time. Phase 4b. Deploy Bean and Use in Applications Place application, Beans and required software on target platform

  5. 5/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Amenities Afforded by Bean Environments • Detection of the Bean’s properties Read only – or- Writeable • Detection of listeners supported So events on the Bean can be handled • Ability to easily create instances and display an image if an awt or swing object Set property values visually • Ability to store instances

  6. 6/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP 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

  7. 7/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Required Bean Rules 2 of 2 • To have property myProp, include methods: <type> getMyProp(){ … } // to access myProp void setMyProp( <type> p ) // to change • Forbooleanproperty: booleanisMyProp() • Name for event classes to be XXXEvent • extends Event • Listeners must implement java.util.EventListener • Name must end in Listener as in XXXListener • added withpublic voidaddXXXListener(...) • removed withpublic voidremoveXXXListener(...)

  8. 8/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP 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 file 11.3 Name: Bean0.class Java-Bean: True

  9. 9/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Bean0 source code public class Bean0 implements java.io.Serializable // required for Beans { private intmyInt = 0; // ("myInt" is not necessarily a property yet!) public Bean0() // Null constructor presence required for all Beans { } public intgetIntgr() // Introduces property "intgr" and makes gettable { return myInt; } public void setIntgr( intanInteger ) // Makes property "intgr" settable { myInt = anInteger; } }

  10. 10/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP JAR’ing a Bean jar cfm Bean0.jar manifest.txt Bean0.class List all .class files to be included Creating a JAR file Second argument is name of manifest file First argument is name of the new JAR file

  11. 11/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP BeanBox Environment

  12. 12/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Adding a Bean to the BeanBox

  13. 13/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Bean1

  14. 14/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Bean1 source code import 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 // properties public 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 BeanBox public 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 down g.fillRect( 30,5,20,30 ); // Write "HELLO WORLD" in the // foreground color g.setColor( getForeground() ); g.drawString( "HELLO WORLD", 5, 20 ); } }

  15. 15/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Setting Color

  16. 16/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP 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

  17. 17/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Phase 3: creating bean instance • BeanBox helps the user to create instances of Bean classes by allowing the user to set some properties visually. 11.5 (green in color)

  18. 18/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Phase 4: combining and deploying beans • Phase 4a: combining Beans in Bean environment • Beginning to Use ChairMaker

  19. 19/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Phase 4: combining and deploying beans • Phase 4a: combining Beans in Bean environment • Setting ChairMaker to Add a Chair Leg

  20. 20/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Phase 4: combining and deploying beans • Phase 4a: combining Beans in Bean environment, • An Output Of ChairMaker Bean

  21. 21/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Phase 4: combining and deploying beans • Phase 4a: combining Beans in Bean environment • Output Of ChairMaker Bean From Button Action

  22. 22/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Phase 4: combining and deploying beans KEY CONCEPT Reusability • Phase 4b: using Beans in applications: Output We want to associate Beans even when there is no external event such as a mouse click. Object bean1 = Beans.instantiate(null, “Bean1”); Bean1 bean2 = (Bean1)objectInputStream.readObject();

  23. 23/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Connecting Beans via property changes: “bound” variables 11.7 Property Change Event Demonstration

  24. 24/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Connecting Beans via property changes: “bound” variables • Property Change Event Demonstration (cont...)

  25. 25/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Connecting beans via property changes: “bound” variables KEY CONCEPT Bound Properties • bound property demonstration -- causes a Beans to react when a property in another Bean changes value.

  26. 26/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Embedding Beans in JSP <jsp:useBean id="object name" 1 scope="page|request|session|application" 2 class="fully qualified classname" 3 </ jsp:useBean > • 1 Bean instance name as in MyClassmyName = …. • 2 // Choose one; when instance is destroyed; optional; default is page • 3 // e.g., a.b.MyClass 11.8

  27. 27/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP 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

  28. 28/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP Setting and Getting a Bean Property in a JSP: Introduction • <jsp:setProperty • name=“account17" • property=“bal" • value=“3211“ • /> • <jsp:getProperty • name=“account17" • property=“bal" • />

  29. 29/29 Intro Creating Bean Classes Multiple-Class Beans Deploying Beans Connecting Beans Beans in JSP 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

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