attribute is a Java object that servlet code can
bind, or store, in a certain
scope, such as a
ServletContext, a session, or a request. The
object can temporarily store and share a small piece of data in a way
that is not otherwise available to servlet developers. Then, when the
application no longer has use for the object, your code can remove,
or unbind it, and the web container makes the
object available for garbage collection.
This chapter describes how to work with attributes in all three
scopes: ServletContext, session, and request. If
you need to make an object available to all of the servlets and JSPs
in a context, then you can bind the object to a
ServletContext. If the application calls for an
object such as a "shopping cart" to
be bound to a session (see Chapter 11), you can set
the object as a session attribute. Finally, if the application
requires two servlets that communicate via a
RequestDispatcher to share an object, then the
servlets can use an object attribute bound to a request scope.
Since sessions and requests are associated with numerous users in a
busy web application, developers have to pay attention to the size
and resource use of any objects that are bound as attributes to
requests or sessions.