Learn Java for Web Development

82 CHAPTER 2: Building Web Applications Using Servlets and JSP

Listing 2-20. Usage of Common Implicit Objects

1.getServletContext().setAttribute("book", book);
2.request.setAttribute("book", book);
3.request.getSession().setAttribute("book", book);
4.application.setAttribute("book" book);
5.request.setAttribute("book" book);
6.session.setAttribute("book" book);
7.pageContext.setAttribute("book" book);

   Line 1: This sets the book attribute in a ServletContext without using implicit

objects.

   Line 2: This sets the book attribute in a request object. The request object is

also an implicit object in JSP. Hence, setting the attribute in a servlet is similar to

setting the attribute in a JSP page.

   Line 3: This sets the book attribute in the session without using implicit objects.

   Line 4: This sets the book attribute in the ServletContext using the application

implicit object.

   Line 5: This sets the book attribute in a request object. request is also an implicit

object in JSP. Hence, setting the attribute in JSP is similar to setting the attribute

in a servlet.

   Line 6: This sets the book attribute in the session using a session implicit object.

   Line 7: This sets the book attribute in PageContext using a pageContext implicit

object. There is no equivalent of pageContext in a servlet. A PageContext

instance provides access to all the namespaces associated with a JSP

page, provides access to several page attributes, and provides a layer above

the implementation details. Implicit objects are added to the pageContext

automatically.

Standard Actions

The JSP standard actions provide a way to do the following:

   Manipulate JavaBeans

   Dynamically include files

   Perform URL forwarding

The Action

The action provides a way to include at runtime the directive for including the
contents of a separate web component in the declaring JSP page. The syntax for using the standard
include action is as follows: