ServletContextEvent ServletInputStream

HttpSessionEvent

修改会话对象时会触发HttpSessionEvent事件。此事件的相应监听器接口是HttpSessionListener。

我们可以在此事件中执行一些操作，例如计算总登录用户数和当前登录用户数，维护用户详细信息的日志，例如登录时间，注销时间等。

1 HttpSessionListener的方法

HttpSessionListener接口中声明了两种方法，必须由开发者实现这些方法才能执行某些操作。

public void sessionCreated(HttpSessionEvent e): 创建会话对象时调用。
public void sessionDestroyed(ServletContextEvent e): 会话无效时，该方法将被调用。

2 HttpSessionListener案例

在下面的示例中，我们使用HttpSessionListener监听器来统计总登录用户数和当前登录用户数。

2.1 编写页面

index.jsp:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <meta charset="UTF-8">
    <title>一点教程网-HttpSessionListener的使用</title>
    <meta http-equiv="content-type" content="text/html" charset="UTF-8">
</head>
<body>
<form action="servlet1" method="post">
    用户名:<input type="text" name="username"><br>
    密码:<input type="password" name="userpass"><br>
    <input type="submit" value="登录"/>
</form>
</body>
</html>

2.2 编写统计登录用户监听器

LoginUserListener:

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;

/**
 * 一点教程网 - http://www.yiidian.com
 */
public class LoginUserListener  implements HttpSessionListener {
    ServletContext ctx=null;
    static int total=0,current=0;

    public void sessionCreated(HttpSessionEvent e) {
        total++;
        current++;

        ctx=e.getSession().getServletContext();
        ctx.setAttribute("totalusers", total);
        ctx.setAttribute("currentusers", current);

    }

    public void sessionDestroyed(HttpSessionEvent e) {
        current--;
        ctx.setAttribute("currentusers",current);
    }

}

2.3 编写登录Servlet

LoginServlet:

import java.io.*;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.servlet.*;
import javax.servlet.http.*;

/**
 * 一点教程网 - http://www.yiidian.com
 */
public class LoginServlet extends HttpServlet{

    public void doPost(HttpServletRequest request,HttpServletResponse response)
            throws ServletException,IOException
    {
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        String n=request.getParameter("username");
        out.print("欢迎 "+n);

        HttpSession session=request.getSession();
        session.setAttribute("uname",n);

        //retrieving data from ServletContext object
        ServletContext ctx=getServletContext();
        int t=(Integer)ctx.getAttribute("totalusers");
        int c=(Integer)ctx.getAttribute("currentusers");
        out.print("<br>总登录用户数= "+t);
        out.print("<br>当前登录用户数= "+c);

        out.print("<br><a href='logout'>注销</a>");

        out.close();

    }

}

2.4 编写注销Servlet

LogoutServlet:

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 java.io.IOException;
import java.io.PrintWriter;

/**
 * 一点教程网 - http://www.yiidian.com
 */
public class LogoutServlet extends HttpServlet{

    public void doGet(HttpServletRequest request,HttpServletResponse response)
            throws ServletException,IOException
    {
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        HttpSession session=request.getSession(false);
        session.invalidate();//会话失效

        out.print("你已经成功注销登录");


        out.close();

    }

}

2.5 配置web.xml

web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">

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

    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/servlet1</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>LogoutServlet</servlet-name>
        <servlet-class>LogoutServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>LogoutServlet</servlet-name>
        <url-pattern>/logout</url-pattern>
    </servlet-mapping>

    <!--配置监听器-->
    <listener>
        <listener-class>LoginUserListener</listener-class>
    </listener>
</web-app>

2.6 运行测试