1.4.3

Objects and Scopes

A JSP page can create and/or access some Java objects when processing a request.  The JSP 

specification indicates that some objects are created implicitly, perhaps as a result of a 

directive (see Section 2.8,  Implicit Objects ); other objects are created explicitly through 

actions; objects can also be created directly using scripting code, although this is less 

common. The created objects have a 

scope attribute 

defining 

where

 there is a reference to the 

object and 

when

 that reference is removed

.

The created objects may also be visible directly to the scripting elements through some 

scripting level variables (see Section 1.4.7,  Objects and Variables ).

Each action and declaration defines, as part of its semantics, what objects it defines, with 

what scope attribute, and whether they are available to the scripting elements.

Objects are always created within some JSP page instance that is responding to some 

request

object. There are several scopes:

page

   Objects with 

page

 scope are accessible only within the page where they are 

created. All references to such an object shall be released after the response is sent back 

to the client from the JSP page or the request is forwarded somewhere else. References to 

objects with 

page

 scope are stored in the 

pageContext

 object.

request 

  Objects with 

request

 scope are accessible from pages processing the same 

request where they were created. All references to the object shall be released after the 

request is processed; in particular, if the request is forwarded to a resource in the same 

runtime, the object is still reachable. References to objects with 

request

 scope are stored 

in the 

request

 object.

session

   Objects with 

session

 scope are accessible from pages processing requests that 

are in the same session as the one in which they were created. It is not legal to define an 

object with session scope from within a page that is not session aware (see Section 2.7.1, 

 The page Directive ). All references to the object shall be released after the associated 

session ends. References to objects with 

session

 scope are stored in the 

session

 object 

associated with the page activation.

application

   Objects with 

application

 scope are accessible from pages processing 

requests that are in the same application as they one in which they were created. All 

references to the object shall be released when the runtime environment reclaims the 

ServletContext

. Objects with application scope can be defined (and reached) from 

pages that are not session aware. References to objects with 

application

 scope are stored 

in the 

application

object associated with a page activation.

A 

name

 should refer to a unique object at all points in the execution, i.e. all the different 

scopes really should behave as a single name space. A JSP container implementation may or 

not enforce this rule explicitly due to performance reasons.

Chapter 1

Overview

24