1. Persistence & Bean Properties
Properties in Beans
Accessors & Mutators
Indexed & Bound properties
Constrained properties
Examples…
Persistence in JavaBeans
Java Object Serialization
The java.io.Serializable Interface
Versioning
Validating Objects
The java.io.Externalizable Interface
The topics of Persistence and Properties in JavaBeans is considered . The subtopics in each of them is listed.
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CS6704: Design Patterns & Component Frameworks, Spring 2002

2. CS6704: Design Patterns & Component Frameworks, Spring 2002
What is a Property?
Named attributes / characteristics that define the behavior & state of the object (bean)
How is it different from a variable?
Bean
Bean
Properties
Bean actions tied to properties
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CS6704: Design Patterns & Component Frameworks, Spring 2002

3. Design Patterns (coding convention)
Why?
Accessors
function to get value of a variable, no params.
<property type> <property name>;
<property type> get<property name>( ) ;
Example:
public class Temperature {
protected double currentTemperature = 25;
public double getCurrentTemperature() {
return currentTemperature; }
public boolean is<PropertyName>( );
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CS6704: Design Patterns & Component Frameworks, Spring 2002

4. CS6704: Design Patterns & Component Frameworks, Spring 2002
Mutators:
Functions that change the value of a property
Takes parameters
Design pattern:
public void set<property name>(<property type> value) ;
Example:
public class Temperature {
protected double currentTemperature = 25;
public double setCurrentTemperature(double cTemp) {
currentTemperature = cTemp; }
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CS6704: Design Patterns & Component Frameworks, Spring 2002

5. Indexed & Bound properties:
Design pattern – indexed property:
* public <PropertyType>[] get<PropertyName>( );
public void set<PropertyName> ( <PropertyType>[] value );
* public <PropertyType> get<PropertyName> (int index);
public void set<PropertyName> (int index, <PropertyType> value);
(Hint: java.lang.ArrayIndexOutOfBoundsException should be thrown !)
Bound properties – support change notifications
PropertyChangeListener & PropertyChangeEvent
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CS6704: Design Patterns & Component Frameworks, Spring 2002

6. Bound properties… Property Owner propertyChange( )
Notifying a listener about a change in property:
addPropertyChangeListener
removePropertyChangeListener
Bean 1
Property Owner
(producer)
Property 1 Changed
Property 2 Changed …
Property n Changed
PropertyChangeEvent
PropertyChangeEvent
PropertyChangeEvent
propertyChange( )
Bean 2
PropertyChangeListener
(consumer)
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CS6704: Design Patterns & Component Frameworks, Spring 2002

7. java.beans.PropertyChangeEvent
Constructor:
public PropertyChangeEvent (Object sourceBean, String propertyName, Object oldValue, Object newValue );
Methods:
public Object getNewValue ( );
public Object getOldValue ( );
public String getPropertyName( );
public Object getPropagationId ( );
public Object setPropagationId ( Object newId );
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CS6704: Design Patterns & Component Frameworks, Spring 2002

8. java.beans.PropertyChangeSupport – utility class
Listener
Bean
Properties
Listener
Property Support
Listener
public PropertyChangeSupport ( Object sourceBean )
public synchronized void addPropertyChangeListener (PropertyChangeListener newListener )
public synchronized void addPropertyChangeListener (PropertyChangeListener existingListener )
public void firePropertyChange ( String propertyName, Object oldValue, Object newValue )
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CS6704: Design Patterns & Component Frameworks, Spring 2002

9. Constrained Properties:
Change rejected
setProperty( )
Bean
Constrained property
PropertyVetoException
vetoableChange( )
Change rejected
VetoableChangeListeners
VetoableChangeListener
Public abstract void vetoableChange( PropertyChangeEvent vetoablePropertyEvent )
throws PropertyVetoException
PropertyVetoException
public PropertyVetoException (String reasonForVeto, PropertyChangeEvent eventVetoed )
VetoableChangeSupport
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CS6704: Design Patterns & Component Frameworks, Spring 2002

10. CS6704: Design Patterns & Component Frameworks, Spring 2002
Application
Persistent State
Persistent
Storage
Persistence!
Save
Restore
Object Serialization – java.io package
java.io.FileInputStream & java.io.FileOutputStream
Java.io.ObjectInputStream & java.io.ObjectOutputStream
Socket
File
Object
Stream
Serialized State
Object Stream source and target may vary…
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CS6704: Design Patterns & Component Frameworks, Spring 2002

11. CS6704: Design Patterns & Component Frameworks, Spring 2002
An example…
//save a String and double to the stream
String str = “Sample”;
double d = 3.14;
FileOutputStream fos = new FileOutputStream (“Beans.ser”);
ObjectOutputStream oos = new ObjectOutputStream (fos);
oos.writeObject (str);
oos.writeObject (d);
oos.flush();
// restore the String and double
FileInputStream fis = new FileInputStream (“Beans.ser”);
ObjectInputStream ois = new ObjectInputStream (fis);
String str = (String) ois.readObject();
double d = s.readDouble();
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CS6704: Design Patterns & Component Frameworks, Spring 2002

12. java.io.Serializable interface:
No methods
Just a marker, indicating class is serializable
Object / Class tree traversed to serialize
java.io.NotSerializableException thrown, if unserializable member found
Static and Transient members not serialized
import java.io.*; Saver.java
import java.awt.*;
public class Saver {
Saver() {
Button b = new Button("Bean Button");
b.setFont(new Font("System", Font.BOLD, 20));
try {
FileOutputStream f = new FileOutputStream ("Saver.ser");
ObjectOutputStream o = new ObjectOutputStream (f);
o.writeObject(b);
o.flush();
}catch (Exception e){ System.out.println(e); } }
public static void main (String a[ ]) {
new Saver();
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CS6704: Design Patterns & Component Frameworks, Spring 2002

13. CS6704: Design Patterns & Component Frameworks, Spring 2002
Reader.java
//<applet code="Reader" height=100 width=200></applet>
import java.applet.*;
import java.io.*;
import java.awt.*;
public class Reader extends Applet {
public void init() {
try {
FileInputStream f = new FileInputStream ("Saver.ser");
ObjectInputStream o = new ObjectInputStream (f);
Button b = (Button)o.readObject();
add(b);
} catch (Exception e) {
System.out.println(e); }
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CS6704: Design Patterns & Component Frameworks, Spring 2002

14. CS6704: Design Patterns & Component Frameworks, Spring 2002
Versioning:
inevitable tendency for an object to evolve over time and gain new functionality
New version (vs.) old version conflict
Compatible changes:
Do not render serialized data unusable by older class
 Adding new methods
 Changing the base class
java.io.InvalidClassException thrown
serialver <class name> - generates a SUID (Stream Unique ID )
E.g., > serialver Reader
Reader: static final long serialVersionUID = L;
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CS6704: Design Patterns & Component Frameworks, Spring 2002

15. java.io.Externalizable interface:
How is it different from Serializable interface?
writeExternal ( ) and readExternal ( )
Class hierarchy not traversed during serialization
Versioning – responsibility of the object
Instantiating Serialized Objects:
the instantiate( ) method in java.beans.Beans (static)
2 parameters: class loader, bean’s fully qualified name
If 1st parameter = null -> uses default class loader
Instantiate() – looks for a “pickled” bean, if not found uses “new” to create an instance
Requires that the bean have constructor with no params.
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CS6704: Design Patterns & Component Frameworks, Spring 2002

16. CS6704: Design Patterns & Component Frameworks, Spring 2002
References:
Developing JavaBeans – Robert Englander
( O’Reilly publications )
JavaBeans Developer’s Resource – Prashant Sridharan ( Prentice Hall )
Presenting JavaBeans – Michael Morrison
(MCP , Sams publishing )
JavaBeans Developer's Guide – Piroz Mohseni
- ( IDG Books worldwide )
Questions ?!!
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CS6704: Design Patterns & Component Frameworks, Spring 2002