监听器Listener

时间：2021-03-24 13:03:42

监听器

6个事件类，均以event结尾
*某些操作，如启动/关闭容器，创建/销毁会话，都将触发一种事件发生，当发生了某种事件，容器将创建对应的事件类对象
8个监听接口，均以Listener结尾
监听器定义了监听方法，可以处理对应的事件

ServletAPI中的6个事件类：
ServletContextEvent：该类表示上下文（ServletContext）事件，当应用上下文对象发生变化，如创建或销毁上下文对象时，将触发上下文事件
ServletContextAttributeEvent：该类表示上下文（ServletContext）属性事件，当应用上下文属性改变，例如增加、删除、覆盖上下文中的属性时，将触发上下文属性事件
ServletRequestEvent：该类表示请求（ServletRequest）事件，当请求对象发生改变，例如创建或者销毁请求对象，将触发此事件
ServletRequestAttributeEvent：该类表示请求（ServletRequest）属性事件，当请求中的属性发生改变，触发该事件
HttpSessionEvent：该类表示会话（HttpSession）事件，当会话对象发生改变，例如创建或者销毁会话对象，活化或者钝化会话对象，将触发此事件
HttpSessionBindingEvent：该类表示会话（HttpSession）绑定事件，当会话中的属性发生变化，例如增加删除覆盖会话中

Servlet API针对每种事件类型，都定义了至少一种借口来处理该事件，这些接口都以Listener结尾，成为监听器接口，共有如下8种接口。
ServletConetxListener：上下文监听器，监听ServletContextEvent事件
ServletContextaAttributeListener：上下文属性监听器，用来监听ServletRequestAttributeEvent事件
ServletRequestListener：请求监听器，监听ServletRequestEvent事件。
ServletRequestAttributeListener:请求属性监听器，用来监听ServletRequestAttributeEvent事件
HttpSessionListener：会话监听器，监听HttpSessionEvent事件
HttpSessionActivationListener：会话活化监听器，监听HttpSessionEvent事件
HttpSessionAttributeListener：会话属性监听器，监听HttpSessionBindingEvent事件
HttpSessionBindingListener：会话绑定监听器，监听HttpSessionBindingEvent事件。

使用监听器的小例子：

计算登录次数：　

package cn.itcast.service;

import javax.servlet.ServletContext;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

public class CounterListener implements ServletContextListener{

    public void contextDestroyed(ServletContextEvent arg0) {

        System.out.println("我是销毁方法");

        ServletContext context=arg0.getServletContext();

        CounterService countService=new CounterService();

        countService.saveNub((Integer) context.getAttribute("counter"));

    }

    public void contextInitialized(ServletContextEvent arg0) {

        ServletContext context=arg0.getServletContext();

        CounterService countService=new CounterService();

        context.setAttribute("counter",countService.getNub() );

    }

}

<listener>

      <listener-class>cn.itcast.service.CounterListener</listener-class>

  </listener>

使用监听器开发的步骤：

　　1、根据实际情况，选择需要使用的监听器，如监听上下文对象创建或销毁的事件，则使用ServletContextListener

　　2、创建新的类，实现选择的监听器接口，兵书写具体实现代码

　　3、在web.xml中配置监听器

上面的例子全貌：

create table counter

(

       nub integer not null unique

)

package cn.itcast.dao;

import org.hibernate.Query;

import org.hibernate.Session;

import cn.itcast.domain.Counter;

import cn.itcast.utils.SessionFactoryUtil;

public class CounterDao {

    public Session getSession(){

        return SessionFactoryUtil.getSession();

    }

    public void saveNub(int nub){

        String hql="update Counter set nub=?";

        Query query=getSession().createQuery(hql);

        query.setParameter(0, nub);

        query.executeUpdate();

    }

    public int getNub(){

        String hql="from Counter";

        Query query=getSession().createQuery(hql);

        Counter count=(Counter) query.uniqueResult();

        return count.getNub();

    }

}

package cn.itcast.domain;

import java.io.Serializable;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Table;

@Table

@Entity

public class Counter implements Serializable{

    private static final long serialVersionUID = 1L;

    private int nub;

    @Column

    public int getNub() {

        return nub;

    }

    public void setNub(int nub) {

        this.nub = nub;

    }

    public Counter(){

    }

    public Counter(int nub){

        this.nub=nub;

    }

}

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">  

<hibernate-mapping>

    <class name="cn.itcast.domain.Counter"

    table="COUNTER">

        <composite-id>

            <key-property name="nub" column="nub" type="java.lang.Integer"/>

        </composite-id>

    </class>

</hibernate-mapping>  

package cn.itcast.service;

import javax.servlet.ServletContext;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

public class CounterListener implements ServletContextListener{

    public void contextDestroyed(ServletContextEvent arg0) {

        System.out.println("我是销毁方法");

        ServletContext context=arg0.getServletContext();

        CounterService countService=new CounterService();

        countService.saveNub((Integer) context.getAttribute("counter"));

    }

    public void contextInitialized(ServletContextEvent arg0) {

        ServletContext context=arg0.getServletContext();

        CounterService countService=new CounterService();

        context.setAttribute("counter",countService.getNub() );

    }

}

package cn.itcast.service;

import org.hibernate.Transaction;

import cn.itcast.dao.CounterDao;

public class CounterService {

    private CounterDao counterDao=new CounterDao();

    public int getNub(){

        return counterDao.getNub();

    }

    public void saveNub(int nub){

        Transaction transaction=counterDao.getSession().beginTransaction();

        try{

            counterDao.saveNub(nub);

            transaction.commit();

        }catch(Exception e){

            e.printStackTrace();

            transaction.rollback();

        }

    }

}

package cn.itcast.test;

import org.junit.Test;

import cn.itcast.service.CounterService;

import cn.itcast.utils.SessionFactoryUtil;

@SuppressWarnings("unused")

public class Test01 {

    @Test

    public void test1() {

        SessionFactoryUtil su=new SessionFactoryUtil();

    }

    @Test

    public void test2(){

        CounterService counterService=new CounterService();

        counterService.saveNub(-1);

        System.out.println(counterService.getNub());

    }    

}

package cn.itcast.utils;

import java.io.IOException;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

/**

 * 字符编码过滤器

 * @author Administrator

 *

 */

public class CharacterEncodingFilter implements Filter{

    private String encoding;

    public void destroy() {

    }

    public void doFilter(ServletRequest arg0, ServletResponse arg1,

            FilterChain arg2) throws IOException, ServletException {

        arg0.setCharacterEncoding(encoding);

        arg1.setCharacterEncoding(encoding);

        arg2.doFilter(arg0, arg1);

    }

    public void init(FilterConfig arg0) throws ServletException {

        this.encoding=arg0.getInitParameter("encoding");

    }

}

package cn.itcast.utils;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;

import org.hibernate.service.ServiceRegistry;

import org.hibernate.service.ServiceRegistryBuilder;

public class SessionFactoryUtil {

    private static SessionFactory factory;

    private static ThreadLocal<Session> threadLocal=new ThreadLocal<Session>();

    static{

        Configuration config=new Configuration().configure();

        ServiceRegistry resgistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();

        factory=config.buildSessionFactory(resgistry);

    }

    public static Session getSession(){

        Session session=threadLocal.get();

        if(session==null){

            session=factory.openSession();

            threadLocal.set(session);

        }

        return session;

    }

}

package cn.itcast.utils;

import java.awt.BasicStroke;

import java.awt.Color;

import java.awt.Font;

import java.awt.Graphics2D;

import java.awt.image.BufferedImage;

import java.io.IOException;

import java.io.OutputStream;

import java.util.Random;

import javax.imageio.ImageIO;

public class VerifyCode {

    private int w=70;

    private int h=35;

    private Random r=new Random();

    private String[] fontNames={"宋体","华文楷体","微软雅体","楷体_GB2312"};

    private String codes="23456789abdcefghjkmnopqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ";

    private Color bgColor=new Color(255,255,255);

    private String text;

    private Color randomColor(){

        int red=r.nextInt(150);

        int green=r.nextInt(150);

        int blue=r.nextInt(150);

        return new Color(red,green,blue);

    }

    public char randomChar(){

        return codes.charAt(r.nextInt(codes.length()));

    }

    private Font randomFont(){

        int index=r.nextInt(fontNames.length);

        String fontName=fontNames[index];

        int style=r.nextInt(4);

        int size=r.nextInt(5)+24;

        return new Font(fontName,style,size);

    }

    private void drawLine(BufferedImage image){

        int num=3;

        Graphics2D g2=(Graphics2D)image.getGraphics();

        for(int i=0;i<num;i++){

            int x1=r.nextInt(w);

            int y1=r.nextInt(h);

            int x2=r.nextInt(w);

            int y2=r.nextInt(h);

            g2.setStroke(new BasicStroke(1.5F));

            g2.setColor(Color.BLUE);

            g2.drawLine(x1, y1, x2, y2);

        }

    }

    private BufferedImage createImage(){

        BufferedImage bi=new BufferedImage(w,h,BufferedImage.TYPE_INT_RGB);

        Graphics2D g2=(Graphics2D)bi.createGraphics();

        g2.setColor(bgColor);

        g2.fillRect(0, 0, w, h);

        return bi;

    }

    private void setText(String text){

        this.text=text;

    }

    public String getText(){

        return text;

    }

    public BufferedImage getImage(){

        BufferedImage image=createImage();

        Graphics2D g2=(Graphics2D)image.createGraphics();

        StringBuilder sb=new StringBuilder();

        for(int i=0;i<4;i++){

            String s=randomChar()+"";

            sb.append(s);

            float x=i*1.0F*w/4;

            g2.setFont(randomFont());

            g2.setColor(randomColor());

            g2.drawString(s, x, h-5);

        }

        this.setText(sb.toString());

        drawLine(image);

        return image;

    }

    public static void output(BufferedImage image,OutputStream out){

        try {

            ImageIO.write(image, "JPEG", out);

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

}

package cn.itcast.web;

import java.awt.image.BufferedImage;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import cn.itcast.utils.VerifyCode;

@SuppressWarnings("static-access")

public class CheckCodeServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doPost(request,response);

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        VerifyCode verify=new VerifyCode();

        BufferedImage image=verify.getImage();

        String text=verify.getText();

        request.getSession().setAttribute("checkCode", text);

        verify.output(image, response.getOutputStream());

    }

}

package cn.itcast.web;

import java.io.IOException;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class LoginServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doPost(request,response);

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        ServletContext context=this.getServletContext();

        String name=request.getParameter("username");

        String password=request.getParameter("password");

        String checkCode=request.getParameter("checkCode");

        String text=(String) request.getSession().getAttribute("checkCode");

        int x=(Integer) context.getAttribute("counter")+1;

        System.out.println(name+"  "+password+" "+checkCode+" "+text);

        context.setAttribute("counter", x);

        request.setAttribute("loginName",name);

        request.getRequestDispatcher("/success.jsp").forward(request, response);

    }

}

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"

        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>

        <!-- Database connection settings -->

        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>

        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:DB</property>

        <property name="connection.username">scott</property>

        <property name="connection.password">961012gz</property>

        <property name="dialect">org.hibernate.dialect.OracleDialect</property>

        <property name="show_sql">true</property>

        <!--

            <mapping class="cn.itcast.domain.Counter"/>

        -->

        <mapping resource="cn/itcast/domain/Counter.hbm.xml"/>

    </session-factory>

</hibernate-configuration>

<?xml version="1.0" encoding="UTF-8"?>

<web-app version="2.5"

    xmlns="http://java.sun.com/xml/ns/javaee"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee

    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

  <display-name></display-name>

  <welcome-file-list>

    <welcome-file>index.jsp</welcome-file>

  </welcome-file-list>

  <servlet>

      <servlet-name>checkCodeServlet</servlet-name>

      <servlet-class>cn.itcast.web.CheckCodeServlet</servlet-class>

  </servlet>

  <servlet>

    <description>This is the description of my J2EE component</description>

    <display-name>This is the display name of my J2EE component</display-name>

    <servlet-name>LoginServlet</servlet-name>

    <servlet-class>cn.itcast.web.LoginServlet</servlet-class>

  </servlet>

  <servlet-mapping>

      <servlet-name>checkCodeServlet</servlet-name>

      <url-pattern>/checkCode</url-pattern>

  </servlet-mapping>

  <servlet-mapping>

    <servlet-name>LoginServlet</servlet-name>

    <url-pattern>/login</url-pattern>

  </servlet-mapping>

  <filter>

      <filter-name>CharacterEncoding</filter-name>

      <filter-class>cn.itcast.utils.CharacterEncodingFilter</filter-class>

      <init-param>

          <param-name>encoding</param-name>

          <param-value>utf-8</param-value>

      </init-param>

  </filter>

  <filter-mapping>

      <filter-name>CharacterEncoding</filter-name>

      <url-pattern>/*</url-pattern>

  </filter-mapping>

  <listener>

      <listener-class>cn.itcast.service.CounterListener</listener-class>

  </listener>

</web-app>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'login.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

    <script>

        function change(){

            var img=document.getElementsByName("img")[0];

            img.src="checkCode?date="+new Date().getTime();

        }

    </script>

  </head>

  <body>

    <form action="login" method="post">

        用户名：<input type="text" name="username"><br/>

        密码：<input type="password" name="password"><br/>

        验证码：<input type="text" size="5" name="checkCode"/><img src="checkCode" name="img"><a href="javascript:void(0)" onclick="change()">刊不清，换一张</a><br/>

        <input type="submit" value="登录">

    </form>

  </body>

</html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'success.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

    欢迎${requestScope.loginName }莅临本系统<br/>

   <p align="right">访问量${applicationScope.counter }</p>

  </body>

</html>

Listener: 监听器
1、初次见面：AWT
2、二次见面：SAX

监听器：
它是一个接口，内容由我们来实现
它需要注册，例如注册在按钮上
监听器中的方法，会在特殊事件发生时被调用！

观察着：
事件源
小偷
事件
偷东西
监听器
警察
监听器中的方法：抓捕

javaWeb中的监听器
事件源：三大域
ServletContext
生命周期监听：ServletContextListener，它有两个方法，一个在出生时调用，一个在死亡时调用；
属性监听：ServletContextAttributeListener，它有三个方法，一个是在添加属性的时候调用，一个是在替换属性的时候调用，一个是在移除属性时调用

HttpSession
生命周期监听：HttpSessionListener，它有两个方法，一个在出生时调用，一个在死亡时调用；
属性监听：HttpSessionAttributeListener，它有三个方法，一个是在添加属性的时候调用，一个是在替换属性的时候调用，一个是在移除属性时调用

ServletRequest
生命周期监听：ServletRequestListener，它有两个方法，一个在出生时调用，一个在死亡时调用；
属性监听：ServletRequestAttributeListener，它有三个方法，一个是在添加属性的时候调用，一个是在替换属性的时候调用，一个是在移除属性时调用

javaWeb中完成编写监听器：
写一个监听器类：要求必须去实现某个监听器接口
注册，是在web.xml中配置来完成

一个生命周期监听和属性监听例子：

package cn.itcast.web.listener;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

/**

 * ServletContext生死监听

 * @author Administrator

 *

 * 可以在这个监听器存放一些在tomcat启动时就要完成的代码！

 *

 */

public class Alistener implements ServletContextListener {

    public void contextDestroyed(ServletContextEvent arg0) {

        System.out.println("我还会再回来的！");

    }

    public void contextInitialized(ServletContextEvent arg0) {

        System.out.println("我胡汉三又回来了");

    }

}

package cn.itcast.web.listener;

import javax.servlet.ServletContextAttributeEvent;

import javax.servlet.ServletContextAttributeListener;

public class Blistener implements ServletContextAttributeListener{

    public void attributeAdded(ServletContextAttributeEvent arg0) {

        System.out.println("您向application中添加了一个名为"+arg0.getName()+",值为："+arg0.getValue()+"的属性");

    }

    public void attributeRemoved(ServletContextAttributeEvent arg0) {

        System.out.println(arg0.getName()+"="+arg0.getValue());//最后一次相见

    }

    public void attributeReplaced(ServletContextAttributeEvent arg0) {

        System.out.println(arg0.getName()+ "="+arg0.getValue()+","+arg0.getServletContext().getAttribute(arg0.getName()));//返回的是之前的值，最后一次相见

    }

}

 <listener>

      <listener-class>cn.itcast.web.listener.Alistener</listener-class>

  </listener>

<listener>

      <listener-class>cn.itcast.web.listener.Blistener</listener-class>

  </listener>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'index.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

      <%

          application.setAttribute("xxx", "XXX");

      %>

    This is my JSP page. <br>

  </body>

</html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'remove.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

      <%

          application.removeAttribute("xxx");

      %>

    This is my JSP page. <br>

  </body>

</html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'repeat.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

    <%

          application.setAttribute("xxx", "YYY");

      %>

  </body>

</html>

另外两个监听：感知监听（与HttpSession相关）
它用来添加到javaBean上，而不是添加到三大域
无需在web.xml注册
HttpSessionBindingListener:添加到javabean上，javabean就知道自己是否添加到session中了

监听bean添加到session的例子：

package cn.itcast.web.listener;

import javax.servlet.http.HttpSessionBindingEvent;

import javax.servlet.http.HttpSessionBindingListener;

public class User implements HttpSessionBindingListener {

    private String username;

    private String password;

    public String getUsername() {

        return username;

    }

    public void setUsername(String username) {

        this.username = username;

    }

    public String getPassword() {

        return password;

    }

    public void setPassword(String password) {

        this.password = password;

    }

    public User() {

        super();

        // TODO Auto-generated constructor stub

    }

    public User(String username, String password) {

        super();

        this.username = username;

        this.password = password;

    }

    public void valueBound(HttpSessionBindingEvent arg0) {

        System.out.println("啊，session添加了我！");

    }

    public void valueUnbound(HttpSessionBindingEvent arg0) {

        System.out.println("啊，无情的session抛弃了我！");

    }

}

<%@ page language="java" import="java.util.*,cn.itcast.web.listener.User" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'add.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

    <%

    User user=new User("gz","6545");

    session.setAttribute("user", user);

    %>

  </body>

</html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'remove.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

    <%

        session.removeAttribute("user");

    %>

  </body>

</html>

session的序列化：
程序有session的时候，意外关闭程序，会自动将session的序列化文件保存起来。重启项目，序列化文件消失，之前的session加载回服务器
存放文件夹例子：E:\anzhuang\tomcat7\apache-tomcat-7.0.70-windows-x86\apache-tomcat-7.0.70\work\Catalina\localhost\8-2_2
文件例子：SESSIONS.ser
废弃session的序列化：
在context.xml中的<Context>标签体内加上
<Manager pathname="" />
Session的钝化和活化：
在一些比较大的网站的时候，访问量过多的话，可能会导致系统占用内存过多。一中利用session钝化优化的手段，就是在context中设置session自动钝化，也就是说在一段时间内，
如果session没有被访问，session就被序列化到硬盘上，再次使用该session的时候，session自动从硬盘上反序列化到内存中。
在Context中设置：
<Manager className="org.apache.catalina.session.PersistentManager" maxIdleSwap="1"><!-- maxIdleSwap代表session的钝化周期，单位分钟 -->
<Store CLASSnAME="org.apache.catalina.session.FileStore" directory="mysession"/><!-- session的序列化文件的存放路径 -->
</manager>

HttpSessionActivationListener:添加到javabean上，监听bean随着session的钝化活化的过程

最后一个监听，监听bean的钝化和活化过程：

package cn.itcast;

import java.io.Serializable;

import javax.servlet.http.HttpSessionActivationListener;

import javax.servlet.http.HttpSessionEvent;

public class User implements HttpSessionActivationListener,Serializable {

    /**

     *

     */

    private static final long serialVersionUID = 1L;

    /**

     * 注意：这个User必须实现序列化接口，否则无法写入硬盘

     */

    public void sessionDidActivate(HttpSessionEvent arg0) {

        System.out.println("啊，~我和session一起重返地球了！");

    }

    public void sessionWillPassivate(HttpSessionEvent arg0) {

        System.out.print("啊，~我陪session去火星了，地球已经不安全了！");

    }

}

<%@ page language="java" import="java.util.*,cn.itcast.User" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'a.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

    <h1>向session中保存数据</h1>

    <%

        session.setAttribute("xxx", "我是一只快乐的小session");

        session.setAttribute("yyy",new User());

    %>

  </body>

</html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

    <title>My JSP 'b.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

  </head>

  <body>

    <h2>获取session中的数据</h2>

    <%

        /* out.print(session.getAttribute("xxx")); */

        out.println(session.getAttribute("yyy"));

    %>

  </body>

</html>

context中的配置：

<Manager className="org.apache.catalina.session.PersistentManager" maxIdleSwap="1">

                <Store className="org.apache.catalina.session.FileStore" directory="mysession"/>

    </Manager>

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