Java Tutorial/Servlet/HttpSessionListener
Servlet HttpSessionListener
<source lang="java">
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import javax.servlet.ServletContext; import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; import javax.servlet.http.HttpSessionAttributeListener; import javax.servlet.http.HttpSessionBindingEvent; import javax.servlet.http.HttpSessionEvent; import javax.servlet.http.HttpSessionListener;
/**
* Example listener for context-related application events, which were * introduced in the 2.3 version of the Servlet API. This listener * merely documents the occurrence of such events in the application log * associated with our servlet context. * * @author Craig R. McClanahan * @version $Revision: 466607 $ $Date: 2006-10-21 17:09:50 -0600 (Sat, 21 Oct 2006) $ */
public final class MyServlet
implements ServletContextListener, HttpSessionAttributeListener, HttpSessionListener {
// ----------------------------------------------------- Instance Variables
/** * The servlet context with which we are associated. */ private ServletContext context = null;
// --------------------------------------------------------- Public Methods
/** * Record the fact that a servlet context attribute was added. * * @param event The session attribute event */ public void attributeAdded(HttpSessionBindingEvent event) { log("attributeAdded("" + event.getSession().getId() + "", "" + event.getName() + "", "" + event.getValue() + "")"); }
/** * Record the fact that a servlet context attribute was removed. * * @param event The session attribute event */ public void attributeRemoved(HttpSessionBindingEvent event) { log("attributeRemoved("" + event.getSession().getId() + "", "" + event.getName() + "", "" + event.getValue() + "")"); }
/** * Record the fact that a servlet context attribute was replaced. * * @param event The session attribute event */ public void attributeReplaced(HttpSessionBindingEvent event) { log("attributeReplaced("" + event.getSession().getId() + "", "" + event.getName() + "", "" + event.getValue() + "")"); }
/** * Record the fact that this web application has been destroyed. * * @param event The servlet context event */ public void contextDestroyed(ServletContextEvent event) { log("contextDestroyed()"); this.context = null; }
/** * Record the fact that this web application has been initialized. * * @param event The servlet context event */ public void contextInitialized(ServletContextEvent event) { this.context = event.getServletContext(); log("contextInitialized()"); }
/** * Record the fact that a session has been created. * * @param event The session event */ public void sessionCreated(HttpSessionEvent event) { log("sessionCreated("" + event.getSession().getId() + "")"); }
/** * Record the fact that a session has been destroyed. * * @param event The session event */ public void sessionDestroyed(HttpSessionEvent event) { log("sessionDestroyed("" + event.getSession().getId() + "")"); }
// -------------------------------------------------------- Private Methods
/** * Log a message to the servlet context application log. * * @param message Message to be logged */ private void log(String message) { if (context != null) context.log("SessionListener: " + message); else System.out.println("SessionListener: " + message); }
/** * Log a message and associated exception to the servlet context * application log. * * @param message Message to be logged * @param throwable Exception to be logged */ private void log(String message, Throwable throwable) { if (context != null) context.log("SessionListener: " + message, throwable); else { System.out.println("SessionListener: " + message); throwable.printStackTrace(System.out); } }
}</source>