JavaServer Faces: Web App Scopes

1
JavaServer Faces Web App Scopes Managed Beans

• Compiled from
• Understanding Scope and Managed Beans
• http//www.netbeans.org/kb/55/vwp-scopes.html
• http//www.netbeans.org/kb/60/web/scopes.html

2
About Scopes

• As long as a user stays on a page, the component
  values are remembered even when the page
  redisplays, such as when the user clicks a button
  that returns null. (when the user leaves the
  page, the component values disappear).
• To make values available to other pages, or to
  make values available to the same page, should
  the user return to it, you need to store the
  values.
• When you create a project from the IDE, the IDE
  creates three managed beans for storing values
• RequestBean1
• SessionBean1
• ApplicationBean1

3
Managed Beans

• a JavaBeans object that a JSF web application
  instantiates and stores in either request scope,
  session scope, or application scope.
• Before you create a bean property to store a
  value, you must determine the appropriate scope
  for the property's value. (Why?)
• The following figure illustrates the duration of
  each type of scope.
• Application scope lasts until the server stops
  the application. Values that you store in an
  application bean are available to every session
  and every request that uses the same application
  map.
• e.g., counter to keep track of all users using
  the app, drop-down list of measurement types for
  all to access
• Session scope begins when a user first accesses a
  page in the web application and ends when the
  session times out due to inactivity, or when the
  web application invalidates the session, such as,
  for example, by calling session.invalidate().
• e.g., users login info, shopping cart
• Request scope begins when the user submits the
  page and ends when the response is fully
  rendered, whatever page that is.
• e.g., anything that is only needed in 1
  request/response cycle (timestamp in the
  programming language voting sample app)

4
Managed Beans

• The web application instantiates a managed bean
  the first time, within that bean's scope, that a
  page accesses a property in the managed bean. For
  example, an instance of a SessionBean1 object
  does not exist for the user's session until the
  user accesses a page that references a
  SessionBean1 property.

5
Language Voting Web App

• http//www.netbeans.org/kb/55/vwp-scopes.html

6
Language Voting Web App (contd)