JavaServer Pages, 3rd Edition

Using an Application Scope Variable

One place for resources that all components in an application need access to is the application scope, corresponding to ServletContext attributes in the servlet world. As I described in Chapter 19, the most appropriate component for initialization and release of this type of shared resources is the application lifecycle listener.

The container informs an application lifecycle listener when the application is started and stopped. It can create the resource objects and make them available to other application components in its contextInitialized( ) method before any user requests are received, and release them when the application is shut down in its contextDestroyed( ) method. Finally, a listener can use configuration data (defined as context parameters in the deployment descriptor) to work in different settings. To recap, here’s an application lifecycle listener similar to the one used in Chapter 19:

package com.ora.jsp.servlets; import javax.servlet.*; import javax.servlet.http.*; import oracle.jdbc.pool.*; public class ResourceManagerListener2 implements ServletContextListener { private OracleConnectionCacheImpl ds = null; public void contextInitialized(ServletContextEvent sce) { ServletContext application = sce.getServletContext( ); String jdbcURL = application.getInitParameter("jdbcURL"); String user = application.getInitParameter("user"); String password = application.getInitParameter("password"); String maxLimit = application.getInitParameter("maxLimit"); ...