CHAPTER 2: Building Web Applications Using Servlets and JSP 81config
Similar to the application object, the config object provides a reference to the ServletConfig
interface of the web application. The ServletConfig interface is used to provide access to any
initialization parameters that have been configured for the JSP page via the deployment descriptor
of the web application. The config object provides the JSP developer with access to the
ServletConfig object.
exception
The implicit exception object is available to JSP to handle the error conditions and report the
runtime exceptions using the errorPage page directive.
out
The implicit out object represents an instance of the JspWriter class that is used to write character
data to the response stream.
page
The JSP implicit page object is an instance of the Object class and represents the current JSP page.
pageContext
A pageContext provides context information by providing access to all the namespaces associated
with a JSP page and to several page attributes. Also, it contains the reference to implicit objects.
request
The request object is an instance of the javax.servlet.http.HttpServletRequest interface.
It represents the client request. The request implicit object is generally used to get request
parameters, request attributes, header information, and query string values.
response
The implicit response object is an instance of the javax.servlet.http.HttpServletResponse
interface and represents the response to be given to the client. The implicit response object is
generally used to set the response content type, add cookies, and redirect the response.
session
The JSP implicit session object is an instance of a Java class that implements the
javax.servlet.http.HttpSession interface. It is used to store session state for a client.
Listing 2-20 illustrates the usage of the often-used implicit objects. First it shows the common task
of setting a book attribute in the request, session, and application scopes in a servlet. Then it shows
their JSP equivalents.