SE452: Implicit Objects and their Scope [2003/10/14]

Objects can be manipulated in JSP.

Objects exist in different scopes:

Remember, and object created inside a method would only have scope in that method as well. In Java, we also limit scope by using the { }

An object with a given scope is accessible to pages that are in the same scope as the page where the object was created. (more on this later)

Certain objects are created implicitly for each page by the container:

request

A reference to the protocol dependent subclass of javax.servlet.ServletRequest (i.e. javax.servlet.http.HttpServletRequest)
You can use it just like you did with servlets
request scope

response

A reference to the protocol dependent subclass of javax.servlet.ServletResponse (i.e. javax.servlet.http.HttpServletResponse)
You can use it just like you did with servlets
page scope

pageContext

an object that provides a context to store references to objects used by the page
encapsulates implementation-dependent features, and provides convenience methods.:
- getOut(), getException(), getPage() getRequest(), getResponse(), getSession(), getServletConfig() and getServletContext().
provides uniform access to diverse objects
- setAttribute(), getAttribute(), findAttribute(), removeAttribute(), getAttributesScope() and getAttributeNamesInScope().
provides methods for inclusion, error handling, and forwarding
- forward(), include(), and handlePageException().
A mechanism for obtaining the JspWriter for output
A single object to manage the various scoped namespaces
page scope

session

A reference to the HTTP session (javax.servlet.http.HttpSession)
You can use it just like you did with servlets.
Only available if this page is marked as participating in a session. (How we do this is later). If it isn't participating, refering to the session is illegal and results in a translation error
session scope

application

The servlet context returned by calling getServletConfig().getContext() in a servlet
You can use it as you would the context in a servlet
application scope

out

javax.servlet.jsp.JspWriter
An object that writes into the output stream like the PrintWriter in a servlet (it is a subclass).
page scope

config

The javax.servlet.ServletConfig that you would get from calling getServletConfig() in a servlet
use for getting init parameters
page scope

page

exception