本案例介绍：

使用监听器来实现踢人小案例，仅仅有管理员才有踢人的功能。

1.搭建开发环境，导入本案例须要的jar包。以及一个准备好的数据库工具类：提供数据源的方法...当中我已经在数据库中加入了三个用户

a:123

b:123

admin:123

package com.itheima.util;

import java.sql.Connection;

import java.sql.SQLException;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class DataSourceUtil {

	private static DataSource source = new ComboPooledDataSource();

	private DataSourceUtil() {

	}

	public static DataSource getSource(){

		return source;

	}

	public static Connection getConn(){

		try {

			return source.getConnection();

		} catch (SQLException e) {

			e.printStackTrace();

			throw new RuntimeException(e);

		}

	}

}

我使用的是c3po的配置文件：

<?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/day14?

generateSimpleParameterMetadata=true</property>

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

    <property name="password">169500</property>

  </default-config>

</c3p0-config>

2.建立主页页面,假设没有登陆就提供登陆的超链接。假设登陆成功就欢迎用户，同一时候提供注销的超链接，和用户列表在线用户的超链接。

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

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

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

<html>

  <head>

    <title></title>

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

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

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

  </head>

  <body>

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

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

    </c:if>

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

    	欢迎${sessionScope.user.name}<a href="${pageContext.request.contextPath }/servlet/LogoutServlet">注销</a><br>

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

    </c:if>

  </body>

</html>

3.开发登陆login.jsp:

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

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

<html>

  <head>

    <title></title>

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

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

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

  </head>

  <body>

    <h1>登录页面</h1><hr>

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

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

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

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

    </form>

  </body>

</html>

执行演示：

4.开发jsp的action的LoginServlet:

步骤：

(1).获取请求參数，我使用的是post提交方式

(2).验证用户和password和数据库中的是不是一直，假设不一致就提示用户信息不存在，假设一致,就把user加入到session域中...

(3).请求转发到主页，欢迎用户...

package cn.itheima.web;

import java.io.IOException;

import java.sql.SQLException;

import java.util.HashMap;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

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 cn.itheima.domain.User;

import com.itheima.util.DataSourceUtil;

public class LoginServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {

		request.setCharacterEncoding("utf-8");

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

		//1.获取请求參数

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

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

		//2.验证密码和数据库中的是否一致

		User user=null;

		try {

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

			String sql="select * from user where name=?

and password=?

";

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

		} catch (SQLException e) {

			e.printStackTrace();

			throw new RuntimeException();

		}

		//3.检验

		if(user==null){

			response.getWriter().write("username不存在！");

		}else{

			//将还有一个同名同密码的用户挤下去

			ServletContext context = this.getServletContext();

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

			HttpSession session = usermap.get(user);

			if(session!=null){

				session.invalidate();

			}

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

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

		}

	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {

		doGet(request, response);

	}

}

5.注销的功能：LogoutServlet

把session中的user干掉就可以

package cn.itheima.web;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class LogoutServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {

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

			request.getSession().invalidate();

		}

		//重定向到主页

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

	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {

		doGet(request, response);

	}

}

6.为了实现踢人的功能：而每一个人登陆的session仅仅是自己的。为了拿到全部用户的session。因此当应用载入完成的时候就在ServletContext域中放一个usermap对象...

我们使用监听器：监听器的配置我就不多说了，在web.xml文件里配置就可以...

package cn.itheima.listener;

import java.util.HashMap;

import java.util.Map;

import javax.servlet.ServletContext;

import javax.servlet.ServletContextEvent;

import javax.servlet.http.HttpSession;

import cn.itheima.domain.User;

public class ServletContextListener implements javax.servlet.ServletContextListener{

	public void contextInitialized(ServletContextEvent sce) {

		ServletContext context = sce.getServletContext();

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

		System.out.println("监听了！..........");

	}

	public void contextDestroyed(ServletContextEvent sce) {

	}

}

7.当用户在session域中放一个user用户的时候我们须要user这个javaBean自己探測到因此须要使用HttpSessionBindingListener接口：

登陆的时候就加入session到application域中。注销的时候就移除..重写hashcode和equal方法为了是username和password同样我们视为同一个对象。

package cn.itheima.domain;

import java.io.Serializable;

import java.util.HashMap;

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 role;

	private String password;

	public String getPassword() {

		return password;

	}

	public void setPassword(String password) {

		this.password = password;

	}

	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 getRole() {

		return role;

	}

	public void setRole(String role) {

		this.role = role;

	}

	//当session中被绑定了对象的时候就往域对象中加入

	public void valueBound(HttpSessionBindingEvent event) {

		HttpSession session = event.getSession();

		ServletContext context = session.getServletContext();

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

		map.put(this, session);

	}

	//注销的时候就移除

	public void valueUnbound(HttpSessionBindingEvent event) {

		HttpSession session = event.getSession();

		ServletContext context = session.getServletContext();

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

		map.remove(this);

	}

	@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;

	}

}

8.在LoginServlet中我们登陆的时候将同username和password的挤下线...见第6步骤

9.编写用户列表：

在这里推断用户是不是admin假设是admin就提供踢人的功能。

这里主要是遍历application域中的在线的用户..

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

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

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

<html>

  <head>

    <title></title>

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

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

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

  </head>

  <h1>用户列表</h1><hr>

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

  		${entry.key.name }

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

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

		</c:if>

		<br>

  	</c:forEach>

</html>

10.编写踢人的servlet，把id带到servlet:

通过id查询出用户然后将其从usermap干掉就可以...

package cn.itheima.web;

import java.io.IOException;

import java.sql.SQLException;

import java.util.HashMap;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

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.itheima.util.DataSourceUtil;

import cn.itheima.domain.User;

public class KickServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {

		//1.获取id

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

		//2.依据id查询用户

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

";

		User user=null;

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

		try {

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

		} catch (SQLException e) {

			e.printStackTrace();

		}

		ServletContext context = this.getServletContext();

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

		 HttpSession session = map.get(user);

		if(session!=null)

		session.invalidate();

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

	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {

		doGet(request, response);

	}

}

11.执行结果分析：

踢人a

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