和request内置对象的监听一样，可以对session的状态和属性进行监听。
1.对session的状态进行监听
要对状态进行监听需要实现的接口是javax.servlet.http.HttpSessionListener

package com.xie.listener;

import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class SessionListener implements HttpSessionListener{
	@Override
	public void sessionCreated(HttpSessionEvent se) {
		System.out.println("创建了session"+se.getSession());
	}

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

@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("访问了servlet方法");
	}

配置session内置对象的状态监听器

<!-- 配置session内置对象的状态监听器 -->
  <listener>
  		<listener-class>com.xie.listener.SessionListener</listener-class>
  </listener>

以上的代码发现了没有创建session对象，原因是没有在servlet中调用getSession()

protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("发送了请求");
		req.getSession();
	}

此时没有处罚销毁的监听方法，因为session对象还没有销毁

@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		req.getSession().invalidate();
	}

以上是对session的状态进行监听，还可以对session的属性进行监听

要实现session属性的监听需要使用到另外一个接口javax.servlet,http.HttpSessionAttributeListener

package com.xie.listener;

import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

public class SessionAttributeListener implements HttpSessionAttributeListener{

	@Override
	public void attributeAdded(HttpSessionBindingEvent event) {
		System.out.println("session增加新的属性："+event.getName()+"="+event.getValue());
	}

	@Override
	public void attributeRemoved(HttpSessionBindingEvent event) {
		System.out.println("session删除了一个属性："+event.getName()+"="+event.getValue());
	}

	@Override
	public void attributeReplaced(HttpSessionBindingEvent event) {
		System.out.println("session替换了一个属性："+event.getName()+"="+event.getValue());
	}

}

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		HttpSession session = req.getSession();
		session.setAttribute("name", "尼古拉斯");
		session.setAttribute("name", "斯巴达");
		session.removeAttribute("name");
	}

  <!-- 配置session内置对象的属性监听器 -->
  <listener>
  		<listener-class>com.xie.listener.SessionAttributeListener</listener-class>
  </listener>