Using Objects Within JSP Pages

You can access a variety of objects, including enterprise beans and JavaBeans components, within a JSP page. JSP technology automatically makes some objects available and you can also create and access application-specific objects.

Implicit Objects

Implicit objects are created by the web container and contain information related to a particular request, page, or application. Many of the objects are defined by the Java Servlet technology underlying the JSP technology.

Table 17 below lists some implicit objects.

Table 17 Implicit Objects 

Variable	Class	Description
application	javax.servlet. ServletContext	The context for the JSP page's servlet and any web components contained in the same application.
config	javax.servlet. ServletConfig	Initialization information for the JSP page's servlet.
exception	java.lang. Throwable	Accessible only from an error page. See Handling Errors.
out	javax.servlet. jsp.JspWriter	The output stream.
request	subtype of javax.servlet. ServletRequest	The request triggering the execution of the JSP page.
response	subtype of javax.servlet. ServletResponse	The response to be returned to the client. Not typically used by JSP page authors.
session	javax.servlet. http.HttpSession	The session object for the client.

Application-Specific Objects

When possible, application behavior should be encapsulated in objects so that page designers can focus on presentation issues. Objects can be created by developers who are proficient in the Java programming language and accessing databases and other services. There are four ways to create and use objects within a JSP page:

• Instance and class variables of the JSP page's servlet class are created in declarations and accessed in scriptlets and expressions.
• Local variables of the JSP page's servlet class are created and used in scriptlets and expressions.
• Attributes of scope objects (see Scope Objects) are created and used in scriptlets and expressions.
• JavaBeans components can be created and accessed using streamlined JSP elements. These elements are discussed in the chapter JavaBeans Components in JSP Pages. You can also create a JavaBeans component in a declaration or scriptlet and invoke the methods of a JavaBeans component in a scriptlet or expression.

Declarations, scriptlets, and expressions are described in JSP Scripting Elements.

From the J2EE Tutorial section on JavaServer Pages Technology by Stephanie Bodoff.

Maintained by John Loomis, last updated 31 March 2001