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13.4 Sharing Beans

305

page

This is the default value. It indicates that, in addition to being 

bound to a local variable, the bean object should be placed in the 

PageContext

 object for the duration of the current request. In 

principle, storing the object there means that servlet code can 

access it by calling 

getAttribute

 on the predefined 

pageContext

 variable. In practice, beans created with 

page

scope are almost always accessed by 

jsp:getProperty

, 

jsp:setProperty

, scriptlets, or expressions later in the same 

page.

application

This very useful value means that, in addition to being bound to a 

local variable, the bean will be stored in the shared 

ServletContext

 available through the predefined 

application

 variable or by a call to 

getServletContext()

. 

The 

ServletContext

 is shared by all servlets in the same Web 

application (or all servlets in the same server or servlet engine if 

no explicit Web applications are defined). Values in the 

ServletContext

 can be retrieved by the 

getAttribute

method. This sharing has a couple of ramifications. 

First, it provides a simple mechanism for multiple servlets and 

JSP pages to access the same object. See the following subsection 

(Conditional Bean Creation) for details and an example. 

Second, it lets a servlet create a bean that will be used in JSP 

pages, not just access one that was previously created. This 

approach lets a servlet handle complex user requests by setting 

up beans, storing them in the 

ServletContext

, then forwarding 

the request to one of several possible JSP pages to present results 

appropriate to the request data. For details on this approach, see 

Chapter 15 (Integrating Servlets and JSP).

session

This value means that, in addition to being bound to a local 

variable, the bean will be stored in the 

HttpSession

 object 

associated with the current request, where it can be retrieved 

with 

getValue

. Attempting to use 

scope="session"

 causes an 

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