Java web之监听器

代码段：

listener.java

package listener;

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


@WebListener
public class listener01  implements HttpSessionListener{
    @Override
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        System.out.println("listener has created````````");
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        System.out.println("listener has destroyed111111111111111");
    }
}

Servlet01

package com.xxx.seervlet;

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 javax.servlet.http.HttpSession;
import java.io.IOException;


@WebServlet("/s01")
public class Servlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("servlet011```````````");
        HttpSession session = request.getSession();
    }
}

Servlet02.java

package com.xxx.seervlet;

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 javax.servlet.http.HttpSession;
import java.io.IOException;


@WebServlet("/s02")
public class Servlet01 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("servlet02```````````");
        request.getSession().invalidate();
    }
}

第一次访问时，触发监听器，打印出监听器已经被创建。同时访问s01.当销毁时，也触发监听器。但是监听器被创建的次数或者机会只有一次，第二次就不会在被创建，除非是要销毁以后。