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An application collects servlets, JSP pages, scripts and Java Beans into a self-contained web application. Applications are just generalized virtual hosts, only based on the URL instead of the host name.

For example, a bulletin board application groups pages for article reading, group listing, user registration, and new article posting into a single application.

Applications can keep track of user sessions, giving the users the illusion of a single application out of disjoint pages.

- Resin organizes applications with an application directory, WEB-INF
- Sessions share state for a user's visit to the site.

Many, if not most sites, will only use the default application.

File/DirectoryContents
.JSP, HTML and GIF files
WEB-INF/classesJava class files
WEB-INF/libJava jars
WEB-INF/tmpTemporary servlet files
WEB-INF/workGenerated java for JSP and XSL

- example
  - index.html
  - folder.gif
  - article.gif
  - post-article.xtp
  - jsp-interest
    - index.jsp
    - article1.jsp
    - article2.jsp
  - WEB-INF
    - lib
      - bulletin-board.jar
    - classes
      - Navigation.class
      - HelloWorld.class
    - xsl
      - default.xsl
      - article.xsl

Java Beans get first class treatment in JSP 1.0. Beans can be created for a page, across a session, or for the entire application.

The classes and lib directories can contain application beans used by jsp:useBean. These are simply Java classes implementing the bitmechanic work of an application.

For example, a shopping cart application may have a set of Java classes that perform the security necessary for credit card processing. The application can put those classes in the beans directory and access them from the JSP page.

Beans can be created with different lifetimes.

- Application beans last the lifetime of an application.
- Session beans last for a user's session.
- Request beans last for a single request.
- Page beans only last for a single page.

Requests and pages often last the same lifetime, but may differ if one page forwards or includes another page.

Each bean is defined with a jsp:useBean directive.

JSP assigns the created bean object to the JavaScript variable named by jsp:useBean.

In addition, the created beans are stored in JSP variables: page beans are stored in ``, session beans are stored in ``, and application beans are stored in ``. Storing the beans in the JSP variables lets other beans and functions retrieve the beans.

<jsp:useBean id='test' class='java.util.Hashtable'> <% test.put("a", 1); %> <%= test.get("a"); %> <jsp:useBean id='test' class='java.util.Hashtable'> <% var t = request.attributes.test t.put("a", 1); %> <%= test.get("a"); %> <results> 1 </results>

Session variables let applications keep track of the user as she moves through the site. Any e-commerce site needs this capability to keep track of the user's purchases.

JSP sessions start when the page accesses the session variable.

Sessions end when the session times out, when the session is invalidated, or when the application ends.