Java Beans

Content What is a Java Bean? BDK What makes Bean possible? Support for Java Bean References

What is a Java Bean?

BDK

What makes Bean possible?

Support for Java Bean

References

What are Java Beans? Software Component Specified interfaces. Independent deployment. Analogy Electronic components. Automotive components.

Software Component

Specified interfaces.

Independent deployment.

Analogy

Electronic components.

Automotive components.

What are Java Beans? ... Definition: “ A Java bean is a reusable software component that can be visually manipulated in builder tools.” Java Bean Tutorials The JavaBeans Specs are available for d/l at http:// java.sun.com/products/javabeans/docs /

Definition:

“ A Java bean is a reusable software component that can be visually manipulated in builder tools.”

Java Bean Tutorials

The JavaBeans Specs are available for d/l at http:// java.sun.com/products/javabeans/docs /

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

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

Software Components “ A software component is a unit of composition with contractually specified interfaces and explicit context dependencies only. A software component can be deployed independently and is subject to composition by third parties.” Szyperski ECOOP96

Composition not Inheritance In OO languages, new objects are created from old using the inheritance mechanism. Pluggable components are connected together by composition rather than inheritance. Most of the flexibility of inheritance can be gained from various compositional tactics.

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

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

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

Software Components Buttons Text Fields List Boxes Scroll Bars Dialogs VBX, OLE

Buttons

Text Fields

List Boxes

Scroll Bars

Dialogs

VBX, OLE

Visually Manipulated, Builder Tools Property Sheet Method Tracer BeanBox ToolBox

BDK...

Selecting the events

Attaching Events

Generating Adapter...

Making an Applet is a click away!

Applet Done!

What makes this possible? Properties Events Persistence Introspection Customization

Properties

Events

Persistence

Introspection

Customization

Properties Attributes. Can be read/write, read-only or write-only. Several types of properties: Simple Indexed Bound Constrained

Attributes.

Can be read/write, read-only or write-only.

Several types of properties:

Simple

Indexed

Bound

Constrained

Design Pattern rules Constructors A bean has a no argument constructor Simple Properties public T getN() public void setN ( T value) Boolean Properties public boolean isN() public boolean getN() public void setN(boolean value) Indexed Properties public T getN(int index) public T[] getN() public void setN(int index, T value) public void setN(T[] values)

Coding examples for Properties public class alden2 extends Canvas { String ourString = “Hello”; public alden2() { setBackground (Color.red); setForeground (Color.blue); } public void setString (String newString) { ourString = newString; } public String getString() { return ourString; } public Dimension getMinimunSize() { return new Dimension (50, 50); } }

public class alden2 extends Canvas {

String ourString = “Hello”;

public alden2() {

setBackground (Color.red);

setForeground (Color.blue);

}

public void setString (String newString) { ourString = newString; }

public String getString() { return ourString; }

public Dimension getMinimunSize() {

return new Dimension (50, 50);

}

}

Bound Properties Generates notification when a property is changed. public class propertDemo extends Canvas { String ourString = “Hello”; private PropertyChangeSupport changes = new PropertyChangeSupport(this); ... public void setString (String newString) { String oldString = ourString; ourString = newString; changes.firePropertyChange(“string”, oldString, newString); } ...

Generates notification when a property is changed.

public class propertDemo extends Canvas {

String ourString = “Hello”;

private PropertyChangeSupport changes = new PropertyChangeSupport(this);

...

public void setString (String newString) {

String oldString = ourString;

ourString = newString;

changes.firePropertyChange(“string”, oldString, newString);

}

...

Bound Properties... ... public void addPropertyChangeListener (PropertyChangeListener l) { changes.addPropertyChangeListener (l); } public void removePropertyChangeListener (PropertyChangeListener l) { changes.removePropertyChangeListener(l); } }

...

public void addPropertyChangeListener (PropertyChangeListener l) {

changes.addPropertyChangeListener (l);

}

public void removePropertyChangeListener (PropertyChangeListener l) {

changes.removePropertyChangeListener(l);

}

}

Constrained Property The concept of a Watcher object. subscribe to the ‘VetoableChange’ Can veto a property change using a PropertyVetoException.

The concept of a Watcher object.

subscribe to the ‘VetoableChange’

Can veto a property change using a PropertyVetoException.

Constrained Property... public class JellyBean extends Canvas { private PropertyChangeSupport changes = new PropertyChangeSupport (this); private VetoableChangeSupport vetos = new VetoableChangeSupport (this); ... public void setColor (int newColor) throws PropertyVetoException { int oldColor = currentColor; vetos.fireVetoableChange(“setColor”, newInteger(oldColor), newInteger(newColor)); currentColor = newColor;

public class JellyBean extends Canvas {

private PropertyChangeSupport changes = new PropertyChangeSupport (this);

private VetoableChangeSupport vetos = new VetoableChangeSupport (this);

...

public void setColor (int newColor) throws PropertyVetoException {

int oldColor = currentColor;

vetos.fireVetoableChange(“setColor”, newInteger(oldColor),

newInteger(newColor));

currentColor = newColor;

Constrained Property... changes.firePropertyChange(“setColor”, new Integer(oldColor), new Integer(newColor)); } public void addVetoableChangeListener (VetoableChangeListener l) { vetos.addVetoableChangeListener(l); } public void removeVetoableChangeListener(VetoableChangeListener l) { vetos.removeVetoableChangeListener(l); } }

changes.firePropertyChange(“setColor”, new Integer(oldColor),

new Integer(newColor));

}

public void addVetoableChangeListener (VetoableChangeListener l) {

vetos.addVetoableChangeListener(l);

}

public void removeVetoableChangeListener(VetoableChangeListener l) {

vetos.removeVetoableChangeListener(l);

}

}

Events Two types of objects are involved: “ Source” objects. “ Listener” objects. Based on registration. Makes use of parametric polymorphism.

Two types of objects are involved:

“ Source” objects.

“ Listener” objects.

Based on registration.

Makes use of parametric polymorphism.

Events Message sent from one object to another. Sender fires event, recipient (listener) handles the event There may be many listeners. Event source Event listener Fire event Event Object Register listener

Message sent from one object to another.

Sender fires event, recipient (listener) handles the event

There may be many listeners.

Event source Event Adapter Fire event Event Object Register event listener Event Listener Forward event Event Object Provide interface

Bean Events Define a new Event class which extends EventObject. XEvent Define a new interface for listeners to implement, this must be an extension of EventListener. XEventListener The Source must provide methods to allow listeners to register and unregister eg addXListener(), removeXListener(). The source must provide code to generate the event and send it to all registered listeners. fireXEvent() The listener must implement the interface to receive the event. changeX() The listener must register with the source to receive the event.

Define a new Event class which extends EventObject. XEvent

Define a new interface for listeners to implement, this must be an extension of EventListener. XEventListener

The Source must provide methods to allow listeners to register and unregister eg addXListener(), removeXListener().

The source must provide code to generate the event and send it to all registered listeners. fireXEvent()

The listener must implement the interface to receive the event. changeX()

The listener must register with the source to receive the event.

Events public class eventSource extends GenericEventGenerator { ... private Vector myListeners = new Vector(); ... public synchronized void addMyEventListeners ( MyEventListener l) { myListeners.addElement(l); } public synchronized void removeMyEventListeners ( MyEventListener l) { myListeners.removeElement(l); } ...

public class eventSource extends GenericEventGenerator {

...

private Vector myListeners = new Vector();

...

public synchronized void addMyEventListeners ( MyEventListener l) {

myListeners.addElement(l);

}

public synchronized void removeMyEventListeners ( MyEventListener l) {

myListeners.removeElement(l);

}

...

Events... private void fanoutEvents() { Vector l; synchronized (this) { l = (Vector) myListener.clone(); } for (int i = 0; i < l.size(); i++) { MyEventListener mel = (MyEventListener) l.elementAt(i); mel.handleThisEvent (this); } }

private void fanoutEvents() {

Vector l;

synchronized (this) {

l = (Vector) myListener.clone();

}

for (int i = 0; i < l.size(); i++) {

MyEventListener mel = (MyEventListener) l.elementAt(i);

mel.handleThisEvent (this);

}

}

Persistence Allows the graphical builder to recall the state of a bean. public class Button implements java.io.Serializable { ... } Selected property fields can bypass the serialization using keywords transient or static .

Allows the graphical builder to recall the state of a bean.

public class Button implements java.io.Serializable { ... }

Selected property fields can bypass the serialization using keywords transient or static .

Persistence... writeObject and readObject private void writeObject (java.io.ObjectOutputStream s) throws java.io.IOException{} private void readObject (java.io.ObjectInputStream s) throws java.io.IOException, java.lang.ClassNotFoundException {} Allows the customization of objects. Appearance and behavior can be stored and recalled. Don’t store references to other beans.

writeObject and readObject

private void writeObject (java.io.ObjectOutputStream s)

throws java.io.IOException{}

private void readObject (java.io.ObjectInputStream s)

throws java.io.IOException, java.lang.ClassNotFoundException {}

Allows the customization of objects.

Appearance and behavior can be stored and recalled.

Don’t store references to other beans.

Introspection A mechanism that allows the builder tool to analyze a bean. Two ways to analyze a bean: low-level reflection APIs. vendor provided explicit information (Customization). Application builder will provide default BeanInfo class <classname>BeanInfo.

A mechanism that allows the builder tool to analyze a bean.

Two ways to analyze a bean:

low-level reflection APIs.

vendor provided explicit information (Customization).

Application builder will provide default BeanInfo class <classname>BeanInfo.

BDK Example package acme.beans; import java.awt.*; import java.io.Serializable; public class Acme04Bean extends Canvas implements Serializable { public Acme04Bean() { resize(60,40); this.label=&quot;Bean&quot;; setFont(new Font(&quot;Dialog&quot;, Font.PLAIN, 12)); }

package acme.beans;

import java.awt.*;

import java.io.Serializable;

public class Acme04Bean extends Canvas implements Serializable {

public Acme04Bean() {

resize(60,40);

this.label=&quot;Bean&quot;;

setFont(new Font(&quot;Dialog&quot;, Font.PLAIN, 12));

}

Introspection... public void paint(Graphics g) { g.setColor(beanColor); g.setColor(Color.blue); int width = size().width; int height = size().height; FontMetrics fm = g.getFontMetrics(); g.drawString(label, (width - fm.stringWidth(label)) / 2, (height + fm.getMaxAscent() - fm.getMaxDescent()) / 2); } public Color getColor() { return beanColor; }

public void paint(Graphics g) {

g.setColor(beanColor);

g.setColor(Color.blue);

int width = size().width;

int height = size().height;

FontMetrics fm = g.getFontMetrics();

g.drawString(label, (width - fm.stringWidth(label)) / 2,

(height + fm.getMaxAscent() - fm.getMaxDescent()) / 2);

}

public Color getColor() {

return beanColor;

}

Introspection... public void setColor(Color newColor) { beanColor = newColor; repaint(); } public String getLabel() { return label; } public void setLabel(String newLabel) { String oldLabel = label; label = newLabel; } private Color beanColor = Color.cyan; private String label; }

public void setColor(Color newColor) {

beanColor = newColor;

repaint();

}

public String getLabel() {

return label;

}

public void setLabel(String newLabel) {

String oldLabel = label;

label = newLabel;

}

private Color beanColor = Color.cyan;

private String label;

}

Introspection...

Customization Similar to Introspection. Develop your own <classname>BeanInfo class which extends SimpleBeanInfo . Develop your own <classname>Editor class which extends PropertyEditorSupport to custom build your property editor.

Similar to Introspection.

Develop your own <classname>BeanInfo class which extends SimpleBeanInfo .

Develop your own <classname>Editor class which extends PropertyEditorSupport to custom build your property editor.

Customization ... <classname>BeanInfo package sun.beanbox.beans; import java.beans.*; public class NervousText07BeanInfo extends SimpleBeanInfo { private final static Class beanClass = NervousText07.class; public BeanDescriptor getBeanDescriptor() { BeanDescriptor bd = new BeanDescriptor(beanClass); bd.setDisplayName(&quot;Uneasy Text 07&quot;); return bd; }

package sun.beanbox.beans;

import java.beans.*;

public class NervousText07BeanInfo extends SimpleBeanInfo {

private final static Class beanClass =

NervousText07.class;

public BeanDescriptor getBeanDescriptor() {

BeanDescriptor bd = new BeanDescriptor(beanClass);

bd.setDisplayName(&quot;Uneasy Text 07&quot;);

return bd;

}

Customization... public PropertyDescriptor[] getPropertyDescriptors() { try { PropertyDescriptor textPD = new PropertyDescriptor(&quot;text&quot;, beanClass); PropertyDescriptor rv[] = {textPD}; textPD.setPropertyEditorClass(NervousText07TextPropertyEditor.class); return rv; } catch (IntrospectionException e) { throw new Error(e.toString()); } } }

public PropertyDescriptor[] getPropertyDescriptors() {

try {

PropertyDescriptor textPD =

new PropertyDescriptor(&quot;text&quot;, beanClass);

PropertyDescriptor rv[] = {textPD};

textPD.setPropertyEditorClass(NervousText07TextPropertyEditor.class);

return rv;

} catch (IntrospectionException e) {

throw new Error(e.toString());

}

}

}

Customization... <classname>Editor package sun.beanbox.beans; import java.beans.*; public class NervousText07TextPropertyEditor extends PropertyEditorSupport { public String[] getTags() { String values[] = { &quot;Nervous Text&quot;, &quot;Anxious Text&quot;, &quot;Funny Text&quot;, &quot;Wobbly Text&quot;}; return values; } }

package sun.beanbox.beans;

import java.beans.*;

public class NervousText07TextPropertyEditor

extends PropertyEditorSupport {

public String[] getTags() {

String values[] = {

&quot;Nervous Text&quot;,

&quot;Anxious Text&quot;,

&quot;Funny Text&quot;,

&quot;Wobbly Text&quot;};

return values;

}

}

BDK Output

Conclusion Easy to use. Difficult to build. Like all OO design, needs careful planning. Similar to the String library in C++. Wide selection of JavaBeans in the future?

Easy to use.

Difficult to build.

Like all OO design, needs careful planning.

Similar to the String library in C++.

Wide selection of JavaBeans in the future?

Support BDK - Sun NetBeans – www.netbeans.org Jbuilder - Inprise Super Mojo - Penumbra Software Visual Age for Java - IBM Visual Cafe - Symantec Corporation JDeveloper Suite - Oracle

BDK - Sun

NetBeans – www.netbeans.org

Jbuilder - Inprise

Super Mojo - Penumbra Software

Visual Age for Java - IBM

Visual Cafe - Symantec Corporation

JDeveloper Suite - Oracle

References http://java.sun.com/products/javabeans/ Java Developer Connection Tutorials Java Beans, Part 1 to 4 http://developer.java.sun.com/developer/onlineTraining/

http://java.sun.com/products/javabeans/

Java Developer Connection Tutorials

Java Beans, Part 1 to 4

http://developer.java.sun.com/developer/onlineTraining/

References... Trail: JavaBeans http://java.sun.com/docs/books/tutorial/javabeans/index.html JavaBeans 1.01 Specification http://java.sun.com/beans/docs/spec.html

Trail: JavaBeans

http://java.sun.com/docs/books/tutorial/javabeans/index.html

JavaBeans 1.01 Specification

http://java.sun.com/beans/docs/spec.html