20160417javaweb之servlet监听器

2022-12-29 15:07:25

监听器：监听器就是一个java程序，功能是监听另一个java对象变化（方法调用、属性变更）

8个监听器,分为了3种
写一个类实现响应的接口
注册监听器 -- 在web.xml中注册监听器

1.用来监听三大作用域的创建和销毁的监听器
ServletContextListener 用来监听ServletContext对象创建和销毁的监听器
创建:服务器启动,web应用加载后立即创建代表当前web应用的ServletContext对象
销毁:服务器关闭或web应用被移除出容器时,随着web应用的销毁而销毁

HttpSessionListener 用来监听HttpSession对象创建和销毁的监听器
创建:第一次调用request.getSession方法时创建代表当前会话的session对象
销毁:超过30分钟没人用销毁/调用invalidate方法自杀/服务器非正常关闭时随着web应用的销毁而销毁,如果服务器是正常关闭会被钝化起来.

当服务器正常关闭时,还存活着的session会随着服务器的关闭被以文件的形式存储在tomcat的work目录下,这个过程叫做session的钝化
当服务器再次正常开启时,服务器会找到之前的SESSIONS.ser文件从中恢复之前保存起来的session对象这个过程叫做session的活化
想要随着Session被钝化活化的对象它的类必须实现Serializable接口

ServletRequestListener 用来监听ServletRequest对象创建和销毁的监听
创建:请求开始创建代表请求的request对象
销毁:请求结束时代表请求的request对象销毁

package com.dzq.listener;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

import javax.servlet.annotation.WebListener;

/**

 * 监听ServletContext创建和销毁的监听器

 * @author

 *

 */

@WebListener

public class MyServletContextListener implements ServletContextListener {

    @Override

    public void contextDestroyed(ServletContextEvent sce) {

        System.out.println("ServletContext对象被销毁了"+sce.getServletContext());

    }

    @Override

    public void contextInitialized(ServletContextEvent sce) {

        System.out.println("ServletContext对象被创建出来了"+sce.getServletContext());

    }

}

package com.dzq.listener;

import javax.servlet.ServletRequestEvent;

import javax.servlet.ServletRequestListener;

import javax.servlet.annotation.WebListener;

@WebListener

public class MySRListener implements ServletRequestListener {

    public void requestDestroyed(ServletRequestEvent arg0)  {

         System.out.println("request对象被销毁"+arg0.getServletRequest());

    }

    public void requestInitialized(ServletRequestEvent arg0)  {

          System.out.println("request对象被创建"+arg0.getServletRequest());

    }

}

package com.dzq.listener;

import javax.servlet.annotation.WebListener;

import javax.servlet.http.HttpSessionEvent;

import javax.servlet.http.HttpSessionListener;

@WebListener

public class MySessionListener implements HttpSessionListener {

    public void sessionCreated(HttpSessionEvent arg0)  {

        System.out.println("session对象被创建"+arg0.getSession());

    }

    public void sessionDestroyed(HttpSessionEvent arg0)  {

        System.out.println("session对象被销毁"+arg0.getSession());

    }

}

2.用来监听三大作用域中属性变化的监听器
ServletContextAttributeListener
HttpSessionAttributeListener
ServletRequestAttributeListener

package com.dzq.listener;

import javax.servlet.annotation.WebListener;

import javax.servlet.http.HttpSessionAttributeListener;

import javax.servlet.http.HttpSessionBindingEvent;

@WebListener

public class MyHSAttribute implements HttpSessionAttributeListener {

    public void attributeAdded(HttpSessionBindingEvent arg0)  { 

    }

    public void attributeRemoved(HttpSessionBindingEvent arg0)  { 

    }

    public void attributeReplaced(HttpSessionBindingEvent arg0)  { 

    }

}

package com.dzq.listener;

import javax.servlet.ServletRequestAttributeEvent;

import javax.servlet.ServletRequestAttributeListener;

import javax.servlet.annotation.WebListener;

@WebListener

public class MyServletAttribute implements ServletRequestAttributeListener {

    public void attributeRemoved(ServletRequestAttributeEvent arg0)  { 

    }

    public void attributeAdded(ServletRequestAttributeEvent arg0)  { 

    }

    public void attributeReplaced(ServletRequestAttributeEvent arg0)  { 

    }

}

package com.dzq.listener;

import javax.servlet.ServletContextAttributeEvent;

import javax.servlet.ServletContextAttributeListener;

import javax.servlet.annotation.WebListener;

@WebListener

public class MySCAttributeListener implements ServletContextAttributeListener {

    public void attributeAdded(ServletContextAttributeEvent arg0)  {

        System.out.println("属性被加进来"+arg0.getName()+arg0.getValue());

    }

    public void attributeRemoved(ServletContextAttributeEvent arg0)  {

         System.out.println("属性被移除"+arg0.getName()+arg0.getValue());

    }

    public void attributeReplaced(ServletContextAttributeEvent arg0)  {

         System.out.println("属性被替换"+arg0.getName()+arg0.getValue());

    }

}

3.使javabean自己感知自己在Session中状态变化的监听器,这两个监听器很特殊,不需要自己去写类实现也不需要在web.xml中注册,只要使javabean实现这个接口就能起作用
HttpSessionBindingListener
javabean被绑定到session中
sessionDidActive(HttpSessionBindingEvent event)
javabean被移除绑定从session中
valueUnbound(HttpSessionBindingEvent event)方法

HttpSessionActivationListener
javabean随着session被钝化
sessionWillPassivate(HttpSessionBindingEvent event)
javabean随着session被活化
sessionDidActive(HttpSessionBindingEvent event)

package com.dzq.domain;

import java.io.Serializable;

import javax.servlet.http.HttpSessionActivationListener;

import javax.servlet.http.HttpSessionBindingEvent;

import javax.servlet.http.HttpSessionBindingListener;

import javax.servlet.http.HttpSessionEvent;

public class Person  implements Serializable ,HttpSessionBindingListener,HttpSessionActivationListener{

  private String username;

public String getUsername() {

    return username;

}

public void setUsername(String username) {

    this.username = username;

}

@Override

public void valueBound(HttpSessionBindingEvent arg0) {

    System.out.println("当前javabean对象被绑定到session域中时，javabean自己感知到自己被绑定，触发此方法");

}

@Override

public void valueUnbound(HttpSessionBindingEvent arg0) {

    System.out.println("当前javabean对象被移除session域中时，javabean自己感知到自己被解绑，触发此方法");

}

//感知被钝化与活化

@Override

public void sessionDidActivate(HttpSessionEvent arg0) {

    System.out.println("javabean自己感知到自己被活化，触发此方法");

}

@Override

public void sessionWillPassivate(HttpSessionEvent arg0) {

    System.out.println("javabean自己感知到自己被钝化，触发此方法");

}

}

踢人小案例：

建立数据库：

package com.dzq.domain;

import java.io.Serializable;

import java.util.Map;

import javax.print.attribute.standard.Severity;

import javax.servlet.ServletContext;

import javax.servlet.http.HttpSession;

import javax.servlet.http.HttpSessionBindingEvent;

import javax.servlet.http.HttpSessionBindingListener;

public class User  implements Serializable,HttpSessionBindingListener{

   private int id;

   private String name;

   private String password;

   private String role;

public int getId() {

    return id;

}

public void setId(int id) {

    this.id = id;

}

public String getName() {

    return name;

}

public void setName(String name) {

    this.name = name;

}

public String getPassword() {

    return password;

}

public void setPassword(String password) {

    this.password = password;

}

public String getRole() {

    return role;

}

public void setRole(String role) {

    this.role = role;

}

@Override

public void valueBound(HttpSessionBindingEvent event) {

    //当用户登录时，bean存入session中，向用户列表添加信息

    HttpSession session=event.getSession();

    ServletContext context= session.getServletContext();

    Map<User,HttpSession> map=(Map<User, HttpSession>) context.getAttribute("usermap");

    map.put(this, session);

}

@Override

public void valueUnbound(HttpSessionBindingEvent event) {

    //当用户下线时，bean移除session中，向用户列表移除信息

    HttpSession session=event.getSession();

    ServletContext context= session.getServletContext();

    Map<User,HttpSession> map=(Map<User, HttpSession>) context.getAttribute("usermap");

    map.remove(this, session);

}

@Override

public int hashCode() {

    final int prime = 31;

    int result = 1;

    result = prime * result + id;

    result = prime * result + ((name == null) ? 0 : name.hashCode());

    return result;

}

@Override

public boolean equals(Object obj) {

    if (this == obj)

        return true;

    if (obj == null)

        return false;

    if (getClass() != obj.getClass())

        return false;

    User other = (User) obj;

    if (id != other.id)

        return false;

    if (name == null) {

        if (other.name != null)

            return false;

    } else if (!name.equals(other.name))

        return false;

    return true;

}

}

User.java

package com.dzq.listener;

import java.util.*;

import javax.servlet.ServletContext;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

import javax.servlet.annotation.WebListener;

import javax.servlet.http.HttpSession;

import com.dzq.domain.User;

@WebListener

public class MySCListener implements ServletContextListener {

    public void contextDestroyed(ServletContextEvent sce)  { 

    }

    public void contextInitialized(ServletContextEvent sce)  {

        ServletContext context=sce.getServletContext();

        context.setAttribute("usermap", new LinkedHashMap<User, HttpSession>());

    }

}

MySCListener

package com.dzq.utils;

import java.sql.Connection;

import java.sql.SQLException;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class DaoUtils {

     private static DataSource source=new ComboPooledDataSource();

     private DaoUtils(){

     }

     public static DataSource getSource(){

         return source;

     }

     public static Connection getConnection(){

         try {

            return source.getConnection();

        } catch (SQLException e) {

            e.printStackTrace();

            throw new RuntimeException(e);

        }

     }

}

DaoUntils

package com.dzq.web;

import java.io.IOException;

import java.sql.SQLException;

import java.util.Map;

import javax.servlet.ServletContext;

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 org.apache.commons.dbutils.QueryRunner;

import org.apache.commons.dbutils.handlers.BeanHandler;

import com.dzq.domain.User;

import com.dzq.utils.DaoUtils;

@WebServlet("/LoginServlet")

public class LoginServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        request.setCharacterEncoding("utf-8");

        response.setContentType("text/html;charset=utf-8");

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

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

        String sql="select * from user where name=? and password =?";

        User user=new User();

        QueryRunner runner=new QueryRunner(DaoUtils.getSource());

        try {

            user=runner.query(sql, new BeanHandler<User>(User.class),name,password);

        } catch (SQLException e) {

            e.printStackTrace();

            throw new RuntimeException(e);

        }

        if(user==null){

            response.getWriter().write("用户名密码不正确");

        }else{

            ServletContext context=this.getServletContext();

            Map<User,HttpSession> map=(Map<User, HttpSession>) context.getAttribute("usermap");

            HttpSession session=map.get(user);

            if(session!=null)

                session.invalidate();

            request.getSession().setAttribute("user", user);

            response.sendRedirect(request.getContextPath()+"/index.jsp");

        }

    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        doGet(request, response);

    }

}

LoginServlet.java

package com.dzq.web;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

@WebServlet("/LogOutServlet")

public class LogOutServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        if(request.getSession(false)!=null){

            request.getSession().invalidate();

        }

        response.sendRedirect(request.getContextPath()+"/index.jsp");

    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        doGet(request, response);

    }

}

LogOutServlet.java

package com.dzq.web;

import java.io.IOException;

import java.sql.SQLException;

import java.util.Map;

import javax.servlet.ServletContext;

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 org.apache.commons.dbutils.QueryRunner;

import org.apache.commons.dbutils.handlers.BeanHandler;

import com.dzq.domain.User;

import com.dzq.utils.DaoUtils;

@WebServlet("/KickServlet")

public class KickServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //获取用户id

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

        User user=null;

        //根据id查询用户

        String sql="select * from user where id =?";

        QueryRunner runner=new QueryRunner(DaoUtils.getSource());

        try {

            user=runner.query(sql, new BeanHandler<User>(User.class),id);

            ServletContext context=this.getServletContext();

            Map<User,HttpSession> map=(Map<User, HttpSession>) context.getAttribute("usermap");

            HttpSession session=map.get(user);

            if(session!=null)

                session.invalidate();

            response.sendRedirect(request.getContextPath()+"/userlist.jsp");

        } catch (SQLException e) {

            e.printStackTrace();

            throw new RuntimeException(e);

        }

        //找到session

        //杀死session

    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        doGet(request, response);

    }

}

KickServlet.java

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

<c3p0-config>

  <default-config>

    <property name="driverClass">com.mysql.jdbc.Driver</property>

    <property name="jdbcUrl">jdbc:mysql://localhost:3306/0417?Unicode=true&amp;characterEncoding=utf-8</property>

    <property name="user">root</property>

    <property name="password"></property>

  </default-config>

</c3p0-config>

c3p0-config.xml

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8"%>

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

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>踢人管理</title>

</head>

<body>

<div align="center">

  <h1>踢人管理系统</h1><hr>

  <c:if test="${sessionScope.user==null }">

  <a href="${pageContext.request.contextPath }/login.jsp">请登录</a>

  </c:if>

  <c:if test="${sessionScope.user!=null }">

             欢迎回来，${sessionScope.user.name }

    <a href="${pageContext.request.contextPath }/userlist.jsp">用户列表</a>

    <a href="${pageContext.request.contextPath}/LogOutServlet">注销</a>

  </c:if>

</div>

</body>

</html>

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>踢人管理</title>

</head>

<body>

<div align="center">

 <h1>踢人管理_用户登录</h1><hr>

 <form action="${pageContext.request.contextPath }/LoginServlet" method="post">

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

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

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

 </form>

</div>

</body>

</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8"%>

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

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>踢人管理系统</title>

</head>

<body>

<div align="center">

  <h1>踢人管理_用户列表</h1><hr>

  <c:forEach items="${applicationScope.usermap }" var="entry">

       ${entry.key.name }<br>

       <c:if test="${sessionScope.user.role=='admin' }">

       <a href="${pageContext.request.contextPath }/KickServlet?id=${entry.key.id}">去死吧</a>

       </c:if>

  </c:forEach>

</div>

</body>

</html>

userlist.jsp

工程结构：

源工程下载：

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