JavaBeans and JSP

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JavaBeans and JSP

• CS-422

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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 .

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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()

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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.

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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
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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

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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))

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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