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356

Chapter 15 Integrating Servlets and JSP

information it needs out of the 

HttpServletRequest

. There are two reasons

why it might not be a good idea to have the destination page look up and pro 

cess all the data itself. First, complicated programming is easier in a servlet

than in a JSP page. Second, multiple JSP pages may require the same data, so

it would be wasteful for each JSP page to have to set up the same data. A bet 

ter approach is for the original servlet to set up the information that the desti 

nation pages need, then store it somewhere that the destination pages can

easily access.

There are two main places for the servlet to store the data that the JSP pages

will use: in the 

HttpServletRequest

 and as a bean in the location specific to

the 

scope

 attribute of 

jsp:useBean

 (see Section 13.4,  Sharing Beans  ).

The originating servlet would store arbitrary objects in the 

HttpServlet 

Request

 by using 

request.setAttribute("key1", value1);

The destination page would access the value by using a JSP scripting ele 

ment to call 

Type1 value1 = (Type1)request.getAttribute("key1");

For complex values, an even better approach is to represent the value as a

bean and store it in the location used by 

jsp:useBean

 for shared beans. For

example, a 

scope

 of 

application

 means that the value is stored in the

ServletContext

, and 

ServletContext

 uses 

setAttribute

 to store values.

Thus, to make a bean accessible to all servlets or JSP pages in the server or

Web application, the originating servlet would do the following:

Type1 value1 = computeValueFromRequest(request);

getServletContext().setAttribute("key1", value1);

The destination JSP page would normally access the previously stored

value by using 

jsp:useBean

 as follows:

Alternatively, the destination page could use a scripting element to explic 

itly call 

application.getAttribute("key1")

 and cast the result to 

Type1

.

For a servlet to make data specific to a user session rather than globally

accessible, the servlet would store the value in the 

HttpSession

 in the nor 

mal manner, as below:

Type1 value1 = computeValueFromRequest(request);

HttpSession session = request.getSession(true);

session.putValue("key1", value1);

The destination page would then access the value by means of

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