20160417javaweb之servlet监听器

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：

使劲点我呀！

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原文地址：https://www.cnblogs.com/xiaoduc-org/p/5400420.html