Java Reference
In-Depth Information
The
application
Object
The
application
object holds a reference to the
javax.servlet.ServletContext
retrieved
from the servlet configuration. The following code snippet, from the JSP's generated servlet,
shows how the
application
object is initialized:
pageContext = _jspxFactory.getPageContext(this, request, response,
“errorpage.jsp”, true, 8192, true);
application = pageContext.getServletContext();
You can see that the generated servlet simply gets a reference to the current
ServletContext
and stores it in the
application
object. The
application
object has application scope, which
means that it is available to all JSPs until the JSP engine is shut down.
The
application
object is most often used to access environment information. Some of the
more common pieces of information accessed by the
application
object are objects that are
stored in the
ServletContext
. These objects are stored there so that they will be available the
whole time the servlet engine is running.
The
ServletContext
is a great place to share objects between JSPs and servlets. In the follow-
ing example, you use the
application
object to store and access our application's specific
information. You will do this by creating a JSP that creates a
Properties
object with the fol-
lowing properties:
PROP1:VAL1
PROP2:VAL2
PROP3:VAL3
You can see that your property object contains three name:value pairs. Next, you will create a
JSP that checks the
application
for a reference to the
Properties
object, by calling the
application.getAttribute()
method with a key that represents the object in the
ServletContext
. If you do not find the referenced object, you will create it and store the
object in the
ServletContext
using the
application.setAttribute()
method. Now the
Properties
object is available to other JSPs and servlets. Listing 15.3 contains this JSP.
L
ISTING
15.3
StoreInApplication.jsp
<%@ page errorPage=”errorpage.jsp” %>
<%@ page import=”java.util.Properties, java.util.Enumeration” %>
<html>
<head>
<title>UseApplication</title>
</head>
<body>
