javabeans (3)

8/8/2019 javabeans (3)

1/19

Java Beans & Serialization

CS-328

Dick Steflik


2/19

Java Beans

Java based component technology

originally developed to provide java with acomponent technology like vbx/ocx of VB

originally used for user interface widgets

currently used forserverside componets

Requirements

Bean naming conventions

must be serializable, to support persistence


3/19

Bean Naming Conventions

setters

set or modify a bean property valuemust start with set

getters

retrieve property values from a bean

must start with get


4/19

Bean Properties Simple

representsasingle property and can be defined with a pair of get/set

methods

Indexed

representsan array of properties

Bound

a bound property notifies other objects when itsvalue changes

generatesa PropertyChange event with property name, old value and new

value

Constrained

an object with constrained propertiesallows other objects to veto a

constrained property value change

Constrained property listeners can veto a change by throwing a

PropertyVetoException


5/19

Interaction Levels

Properties

Bean

Methods

Event


6/19

Bean Framework

Network

Network

Bean

Bean

Bean Bean

Bean

Container Bean


7/19

Introspection

the processby which a builder tool finds out

which properties, methods, and eventsa

bean supports.

searching for classesand methods that follow

certain naming conventions

by querying the BeanInfo ofa class BeanInfo isan interface whose methodsallow the

interrogation ofa beans properties, methodsand

events


8/19

I

ntrospection

Introspector

Methods

Properties

Events


9/19

R

eflection

The core APIs used by the JavaBeans

Introspector class

java.lang.reflect


10/19

a simple GasTank BeanClass Gastank implements Serializable{

private double capacity;

private int percent_full;public void setCapacity(double pounds){

capacity = pounds; }

public double getCapacity() {

return Capacity; }

public void setPercent_full( int p) {

percent_full = p; }

public int getPercent_full() {

return percent_full; }

}


11/19

Jarring the Bean

Beansare packaged in a javaarchive (jar)

file

the jar utility comes with the JDK

the jar file must be explicitly in your class

path

in JDK 1.2.x all AWTand Swing classes

are beans


12/19

GUI

Builders

Because ofa beans naming convention the

GUIs introspector can build a property sheet

for each bean automatically

The GUI builderallows you to configure

the bean as yourapp.Needs

Because the bean isserializable the

configured properties can be saves by the

GUI Builder


13/19


14/19

Persistance

for persistance a bean must implement the

Serializable interface

java.io.Serializable

saving of the beans fields isautomatic, you

need do nothing, everything is done by the

JavaBean API

the same applies to retrieving the beans

persistent values


15/19

Loading and Saving an Object


16/19

Saving an Objectpublic void SaveState(){

FileOutputStream fos = null;ObjectOutputStream oos = null;

try{fos = new

FileOutputStream(State.ser);oos = new

ObjectOutputStream(fos);oos.writeObject(currentState);}

catch(IOException e){System.out.println(e.toString;}

}


17/19

R

estoring an Objectpublic void loadState(){FileInputStream fis = null;ObjectInputStream ois = null

try{fis = newFileInputStream(State.ser);

ois = new ObjectInputStream(fis);State currentState =

(State)ois.readObject();}

catch(ClassNotFoundException e){Systen.out.println(e.toString);}


18/19

public void SaveState(){FileOutputStream fos = null;

ObjectOutputStream oos = null;

try{

fos = new

FileOutputStream(State.ser);oos = new

ObjectOutputStream(fos);

oos.writeObject(currentState);

}catch(IOException e){

System.out.println(e.toString;}}


19/19

For more on JavaBeans

JavaBeans Home Page -

http://java.sun.com/beans/

javabeans (3)

Documents