JavaServer Pages, 3rd Edition

Passing Data from One Page to Another

JSP provides different scopes for sharing data objects between pages, requests, and users. The scope defines how long the object is available and whether it’s available only to one user or to all application users. The following scopes are defined: page, request, session, and application.

Objects placed in the default scope, the page scope, are available only within that page. That’s the scope used in all examples you have seen so far. The request scope is for objects that need to be available to all pages processing the same request, for instance both the page that receives the request initially and the page the first page forwards to. Objects in the session scope are available to all requests made from the same browser, and objects in the application scope are shared by all users of the application (see Figure 10-2). According to the JSP specification, the name used for an object must be unique within all scopes. This means that if you have an object named userInfo in the application scope, for instance, and save another object with the same name in the request scope, the container may remove the first object. Few containers (if any) enforce this rule, but you should ensure you use unique names anyway to avoid portability problems.

Figure 10-2. Lifetime of objects in different scopes

The <jsp:useBean> action has a scope attribute used to ...