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JavaBeans and JSP

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JavaBeans and JSP CS-422 JavaBeans The ... their own persistence this allows the bean to be saved and restored consistently provide a no ... in the whole we ll take ... – PowerPoint PPT presentation

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Title: JavaBeans and JSP


1
JavaBeans and JSP
  • CS-422

2
JavaBeans
  • The Java component technology
  • originally intended for the creation and
    management of pluggable GUI components Javas
    answer to Visual Basics VBX/OCXs
  • becoming more popular for encapsulating business
    logic for server-side applications (especially
    Java Server Pages
  • many Java GUI Development tools have been
    modified to allow application development of
    server-side applications (Visual Café, Jbuilder,
    VisualAge for Java) along with the development
    tools being delivered with application servers
    (SilverStream, BEA Weblogic)
  • A JavaBean is nothing more than a class that
    maintains some state data (called properties) and
    follows a certain set of coding conventions.
    Along with certain Java runtime support
    (reflection and introspection) can JavaBeans can
    be easily added to and maintained by most of the
    Java GUI Development Tools .

3
API requires that
  • Must implement java.io.Serializable or
    java.io.Externalizable
  • Beans must be able to support their own
    persistence
  • this allows the bean to be saved and restored
    consistently
  • provide a no-arguments constructor
  • provides a single way for the Bean to be
    instantiated
  • insures consistent bean creation and
    initialization
  • private properties must have corresponding
    get/set methods that follow the appropriate
    naming patterns
  • each piece of state data to be exposed is called
    a property
  • made public via accessor and mutators (setters
    and getters)
  • accessor methos names must start with get
  • for property int color the accessor would be
    getcolor()
  • mutator methods names must start with set
  • for property fuelCapacity the mutator would be
    setfuelCapacity()

4
Environmental Support
  • To use JavaBeans with JSP no environmental
    support is needed, but for a better understanding
    of JavaBeans in the whole well take a look
  • Introspection ( java.beans.Introspector) defines
    the resources that allow the programatic
    construction of information on the Bean
  • facilitates the discovery of properties and
    methods by inspecting the .class file
  • can be done two ways the reflection APIs or by
    providing a java.beans.BeanInfo class with the
    bean to describe the public methods and
    properties,
  • Reflection (java.lang.reflect) a set of resources
    that allows a program to discover the public
    properties and methods of classes that have been
    loaded by the class loader
  • this is facilitated by the naming convention for
    accessors and mutators (i.e. the names must start
    with get or set)
  • dont need to need to knownames of properties as
    long as we know the names of the accessor and
    mutators
  • These environmental support mechanisma allow the
    JavaBeans to be cleanly integrated into GUI
    based, Java Development tools like VisualCafe,
    VisualAge and Jbuilder.

5
Example a Stock bean
import java.io.Serializable public class Stock
implements Serializable Stock( ) // no
argument constructor (just creates the object)
private String name null private String
tickerSymbol null private double
tradingPrice 0.0 private double
sharesOwned 0.0 public void setName(String
n) name n public String getName( )
return name public void setTickerSymbol(
String s ) tickerSymbol s public
String gettickerSymbol( ) return tickerSymbol
public void settradingPrice( double d )
tradingPrice d public double
gettradingPrice( ) return tradingPrice
public void setsharesOwned( double v )
sharesOwned v public double
getsharesOwned( ) return sharesOwned
6
jspuseBean Tag
  • jspuseBean does the following
  • If the object is found within the specified scope
    it is retrieved and assigned to the object
  • if not found it is instantiated
  • if newly instantiated it executes the code
    specified in the body ( one or more
    jspsetProperty tags or a scriptlet)
  • if newly instantiated it is saved into the scope
    via setAttribute( ) method
  • jspuseBean also makes the bean visible to the
    JSP there may be other objects in the context
    that were put there by other JSPs or servlets
    jspuseBean can make them visible to the current
    JSP

7
jspuseBean Tag (more)
  • Attributes
  • id
  • scope
  • class
  • beanName
  • type
  • ltjspuseBean id today class java.util.Dategt
  • instantiates a bean called today of class
    java.util.Date( )
  • ltjspuseBean id count class
    java.lang.Integer type java.lang.Numbergt
  • essentially does Number count count new
    Integer( )
  • ltjspuseBean id count class lt
    request.getParameter(beanName)gt type
    Number /gt
  • essentiallt does Number count count
    java.beans.Beans.instantiate(request.getParameter(
    beanName))

8
jspuseBean Tag (more)
  • In general the syntax is

ltjspuseBean id name scope page request
session application
class class name class class
name type type name beanName
bean name type type name type
type name /gt
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