JavaWeb -- sevlet 监听器

1.三个域对象的监听（创建和销毁） servletContext,  session, request 监听器

ServletContext监听器：

public class MyServletContextListener implements ServletContextListener {

	@Override
	public void contextInitialized(ServletContextEvent sce) {
		System.out.println("Context 初始化");
	}

	@Override
	public void contextDestroyed(ServletContextEvent sce) {
		System.out.println("Context 销毁");
	}

}

web.xml 配置

<listener>
  	<listener-class>com.kevin.web.listener.MyServletContextListener</listener-class>
</listener>

Session监听器：

public class MyHttpSessionListener implements HttpSessionListener {

	@Override
	public void sessionCreated(HttpSessionEvent se) {
		System.out.println("Session 创建");

	}

	@Override
	public void sessionDestroyed(HttpSessionEvent se) {
		System.out.println("Session 摧毁");
	}

}

Request监听器：

public class MyServletRequestListener implements ServletRequestListener {

	@Override
	public void requestInitialized(ServletRequestEvent sre) {
		System.out.println("request 创建");

	}

	@Override
	public void requestDestroyed(ServletRequestEvent sre) {
		System.out.println("request 销毁");

	}
}

监听器还可以监听三个域中所添加的属性变化：

public class MyServletContextAttributeListener implements
		ServletContextAttributeListener {

	public void attributeAdded(ServletContextAttributeEvent scab) {

		System.out.println(scab.getValue());
		System.out.println("加东西了！！");

	}

	public void attributeRemoved(ServletContextAttributeEvent scab) {
		System.out.println("删东西了！！");
	}

	public void attributeReplaced(ServletContextAttributeEvent scab) {
		System.out.println("替换东西了！！");
	}
}

public class MyRequestAndSessionAttributeListener implements
		HttpSessionAttributeListener, ServletRequestAttributeListener {

	public void attributeAdded(HttpSessionBindingEvent se) {
		System.out.println("session中加东西了！！");
	}

	public void attributeRemoved(HttpSessionBindingEvent se) {
		System.out.println("session中删东西了！！");
	}

	public void attributeReplaced(HttpSessionBindingEvent se) {
		System.out.println("session中替换东西了！！");
	}

	public void attributeAdded(ServletRequestAttributeEvent srae) {
		System.out.println("request中加东西了！！");
	}

	public void attributeRemoved(ServletRequestAttributeEvent srae) {
		System.out.println("request中删东西了！！");
	}

	public void attributeReplaced(ServletRequestAttributeEvent srae) {
		System.out.println("request中替换东西了！！");
	}
}

HttpSessionBindingListener HttpSessionActivationListener 这两个监听器 不需要再web.xml文件中配置

public class MyBean implements HttpSessionBindingListener {

	private String name;

	public void valueBound(HttpSessionBindingEvent event) {
		System.out.println("自己被加到session中了");
	}

	public void valueUnbound(HttpSessionBindingEvent event) {
		System.out.println("自己被session踢出来了");
	}
}

public class MyBean2 implements HttpSessionActivationListener,Serializable {

	public void sessionDidActivate(HttpSessionEvent se) {
		System.out.println("session从硬盘回到内存了");
	}

	public void sessionWillPassivate(HttpSessionEvent se) {
		System.out.println("session被序列化到硬盘了");
	}
}

2. 实例： 在线人数计数器

public class OnLineCountListener implements HttpSessionListener {

	@Override
	public void sessionCreated(HttpSessionEvent se) {

		ServletContext context =  se.getSession().getServletContext();
		Integer num = (Integer) context.getAttribute("num");
		if(num==null)
			context.setAttribute("num", 1);
		else
		{
			num++;
			context.setAttribute("num", num);
		}

	}

	@Override
	public void sessionDestroyed(HttpSessionEvent se) {

		ServletContext context =  se.getSession().getServletContext();
		Integer num = (Integer) context.getAttribute("num");
		if(num==null)
			context.setAttribute("num", 1);
		else
		{
			num--;
			context.setAttribute("num", num);
		}
	}

}

3. 实例： 自定义session扫描器

public class SessionScanerListener implements HttpSessionListener,ServletContextListener {

	private List<HttpSession> list = Collections.synchronizedList( new LinkedList<HttpSession>());
	private Integer lock = 0;	

	@Override
	public void contextInitialized(ServletContextEvent sce) {
		Timer timer = new Timer();
		timer.schedule(new MyTask(list, lock) , 0, 1000*15);

	}

	@Override
	public void sessionCreated(HttpSessionEvent se) {
		HttpSession session =  se.getSession();
		synchronized (lock) {
			list.add(session);
		}
		System.out.println(session + "创建了");
	}

	@Override
	public void sessionDestroyed(HttpSessionEvent se) {
		HttpSession session =  se.getSession();
		System.out.println(session + "销毁了");
	}

	@Override
	public void contextDestroyed(ServletContextEvent sce) {
		// TODO Auto-generated method stub

	}
}

class MyTask extends TimerTask
{
	private List<HttpSession> list;
	private Integer lock;

	public MyTask(List<HttpSession> list, Integer lock)
	{
		this.list = list;
		this.lock = lock;
	}

	@Override
	public void run() {

		synchronized (lock) {
			System.out.println("定时器启动了");
			ListIterator<HttpSession> it = list.listIterator();
			while(it.hasNext())
			{
				HttpSession session = it.next();
				if(System.currentTimeMillis()-session.getLastAccessedTime() > 1000*15)
				{
					session.invalidate();
					list.remove(session);
				}
			}
		}
	}
}