JavaBeans and JSP

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JavaBeans and JSP
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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) JavaBeans can be
  easily added to and maintained by most of the
  Java GUI Development Tools .
• A bean encapsulates data about one entity

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API requires that

• Must implement java.io.Serializable or
  java.io.Externalizable
• A Java bean must be in a package
• 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
• a property is either read-only (has a set),
  write-only (has a get)or read-write (has both)
• a property is case-sensitive and starts with a
  lower-case letter
• made public via accessor and mutators (gets and
  sets)
• accessor method names must start with get
  have no arguments
• for property int color the accessor would be
  getColor() (note cap C)
• mutator method names must start with set and
  return void
• for property fuelCapacity the mutator would be
  setFuelCapacity()

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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)

• Scope of a Java Bean- Four Scopes Available
• Page
• available only within the JSP page and is
  destroyed when the page has finished generating
  its output for the request
• Request
• destroyed when the response is sent
• Session
• destroyed when the session is destroyed
• Application
• destroyed when the web application is destroyed.

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jspuseBean Tag (more)

• In general the syntax is

ltjspuseBean id name scope page request
session application /gt