Building Applications That Keep State
Applications sometimes need to use the result of one request when processing another. For example, a request that adds an item to a shopping cart needs to be remembered when the request is made to create the order. In other words, the state of the application needs to be stored between HTTP requests. There are two ways to achieve this: variables that hold the state can be stored in the browser and included with each request or variables can be stored on the server.
Most of this chapter is devoted to the second alternative, where the middle tier stores and manages the application state using sessions. However, in this section we briefly discuss solutions that store state in the client tier. One technique described in this section is the use of cookies. While cookies can store state in the client tier, they are also used in middle-tier session management, as described later in this chapter.