listener

简介

• 监听ServletContext、HttpSession、ServletRequest等域对象创建和销毁事件
• 监听域对象的属性发生修改的事件
• 监听在事件发生前、发生后做一些必要的处理

1. 创建监听器
2. 监听器内置方法
3. 监听器触发流程

创建一个监控session 的监听器

创建servlet

这个servlet 的作用是创建session 和销毁session

package com.example.listenerdemo.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;


@WebServlet(name = "createSession", value = "/cs")
public class CreateSession extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 创建session
        System.out.println("创建session");
        req.getSession();
    }
}

package com.example.listenerdemo.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;


@WebServlet(name = "destroySession", value = "/ds")
public class DestroySession extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("销毁session");
        req.getSession().invalidate();
    }
}

创建listener

package com.example.listenerdemo.listener;

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

@WebListener
public class SessionListener implements HttpSessionListener {
    @Override
    public void sessionCreated(javax.servlet.http.HttpSessionEvent httpSessionEvent) {
        System.out.println("listener: Session Created");
    }

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

效果