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By - Christen

Scope of JSP Objects

The availability of a JSP object for use from a particular place of the application is defined as the scope of that JSP object. Every object created in a JSP page will have a scope. Object scope in JSP is segregated into four parts and they are page, request, session and application.

page

‘page’ scope means, the JSP object can be accessed only from within the same page where it was created. The default scope for JSP objects created using tag is page. JSP implicit objects out, exception, response, pageContext, config and page have ‘page’ scope.

request

A JSP object created using the ‘request’ scope can be accessed from any pages that serves that request. More than one page can serve a single request. The JSP object will be bound to the request object. Implicit object request has the ‘request’ scope.

session

‘session’ scope means, the JSP object is accessible from pages that belong to the same session from where it was created. The JSP object that is created using the session scope is bound to the session object. Implicit object session has the ‘session’ scope.

application

A JSP object created using the ‘application’ scope can be accessed from any pages across the application. The JSP object is bound to the application object. Implicit object application has the ‘application’ scope.


Form: http://javapapers.com/jsp/explain-the-scope-of-jsp-objects/

What are the different scopes in JSP?

One of the most powerful features of JSP is that a JSP page can access, create, and modify data objects on the server. You can then make these objects visible to JSP pages. When an object is created, it defines or defaults to a given scope. The container creates some of these objects, and the JSP designer creates others.
The scope of an object describes how widely it's available and who has access to it. For example, if an object is defined to have page scope, then it's available only for the duration of the current request on that page before being destroyed by the container. In this case, only the current page has access to this data, and no one else can read it. At the other end of the scale, if an object has application scope, then any page may use the data because it lasts for the duration of the application, which means until the container is switched off.

Page Scope

Objects with page scope are accessible only within the page in which they're created. The data is valid only during the processing of the current response; once the response is sent back to the browser, the data is no longer valid. If the request is forwarded to another page or the browser makes another request as a result of a redirect, the data is also lost.

//Example of JSP Page Scope
<jsp:useBean id="employee" class="EmployeeBean" scope="page" />

Request Scope

Objects with request scope are accessible from pages processing the same request in which they were created. Once the container has processed the request, the data is released. Even if the request is forwarded to another page, the data is still available though not if a redirect is required.

//Example of JSP Request Scope
<jsp:useBean id="employee" class="EmployeeBean" scope="request" />

Session Scope

Objects with session scope are accessible from pages processing requests that are in the same session as the one in which they were created. A session is the time users spend using the application, which ends when they close their browser, when they go to another Web site, or when the application designer wants (after a logout, for instance). So, for example, when users log in, their username could be stored in the session and displayed on every page they access. This data lasts until they leave the Web site or log out.

//Example of JSP Session Scope
<jsp:useBean id="employee" class="EmployeeBean" scope="session" />

Application Scope

Objects with application scope are accessible from JSP pages that reside in the same application. This creates a global object that's available to all pages.
Application scope uses a single namespace, which means all your pages should be careful not to duplicate the names of application scope objects or change the values when they're likely to be read by another page (this is called thread safety). Application scope variables are typically created and populated when an application starts and then used as read-only for the rest of the application.

//Example of JSP Application Scope
<jsp:useBean id="employee" class="EmployeeBean" scope="application" />

From: http://www.java-samples.com/showtutorial.php?tutorialid=1009

Summary

Scope is nothing but lifetime object
1. page - only in the particular jsp
2. request- only in the jsp to which you forward your request object
3. session - it is available until the session is invalidate(you can access it from any jsp)
4. application -it is available until the web application or server shutdown(you can access it from any jsp).available through whole application

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