One of the most powerful features of JSP is that a JSP
page can access, create, and modify data objects on the server. You can then
make these objects visible to JSP pages. When an object is created, it
defines or defaults to a given scope. The container creates some of these
objects, and the JSP designer creates others.
The scope of an object describes how
widely it's available and who has access to it. For example, if an object is
defined to have page scope, then it's available only for the duration of the
current request on that page before being destroyed by the container. In
this case, only the current page has access to this data, and no one else
can read it. At the other end of the scale, if an object has application
scope, then any page may use the data because it lasts for the duration of
the application, which means until the container is switched off.
Objects with page scope are
accessible only within the page in which they're created. The data is
valid only during the processing of the current response; once the
response is sent back to the browser, the data is no longer valid. If the
request is forwarded to another page or the browser makes another request
as a result of a redirect, the data is also lost.
//Example of JSP Page Scope
<jsp:useBean id="employee" class="EmployeeBean" scope="page" />
Objects with request scope
are accessible from pages processing the same request in which they were
created. Once the container has processed the request, the data is
released. Even if the request is forwarded to another page, the data is
still available though not if a redirect is required.
//Example of JSP Request Scope
<jsp:useBean id="employee" class="EmployeeBean" scope="request" />
Objects with session scope
are accessible from pages processing requests that are in the same session
as the one in which they were created. A session
is the time users spend using the application, which ends when they close
their browser, when they go to another Web site, or when the application
designer wants (after a logout, for instance). So, for example, when users
log in, their username could be stored in the session and displayed on
every page they access. This data lasts until they leave the Web site or
//Example of JSP Session Scope
<jsp:useBean id="employee" class="EmployeeBean" scope="session" />
Objects with application scope
are accessible from JSP pages that reside in the same application. This
creates a global object that's available to all pages.
Application scope uses a single namespace, which
means all your pages should be careful not to duplicate the names of
application scope objects or change the values when they're likely to be
read by another page (this is called thread safety).
Application scope variables are typically created and populated when an
application starts and then used as read-only for the rest of the
//Example of JSP Application Scope
<jsp:useBean id="employee" class="EmployeeBean" scope="application" />