大数据必学Java基础（一百一十七）：三个案例开发

原创

Lansonli

发布于 2022-12-23 13:26:43

2970

发布于 2022-12-23 13:26:43

文章被收录于专栏：Lansonli技术博客Lansonli技术博客

三个案例开发

一、记录请求日志

需求：记录每次请求中如下的信息并存储进入日志文件

请求的来源
浏览器所在电脑IP
请求的资源 URL
请求发生的时间

监听器代码

package com.lanson.listener;
import javax.servlet.ServletRequest;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpServletRequest;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintWriter;
import java.text.SimpleDateFormat;
import java.util.Date;
/**
 * @Author: Lansonli
 * @Description: MircoMessage:Mark_7001
 */
@WebListener
public class RequestLogListener implements ServletRequestListener {
    private SimpleDateFormat simpleDateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    @Override
    public void requestDestroyed(ServletRequestEvent sre) {
    }
    @Override
    public void requestInitialized(ServletRequestEvent sre) {
        // 获得请求发出的IP
        // 获得请求的URL
        // 获得请求产生的时间
        HttpServletRequest request = (HttpServletRequest)sre.getServletRequest();
        String remoteHost = request.getRemoteHost();
        String requestURL = request.getRequestURL().toString();
        String reqquestDate = simpleDateFormat.format(new Date());
        // 准备输出流
        try {
            PrintWriter pw =new PrintWriter(new FileOutputStream(new File("d:/lanson.txt"),true));
            pw.println(remoteHost+" "+requestURL+" "+reqquestDate );
            pw.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}

二、统计实时在线人数

需求：

当任何一个账户处于登录状态时,在线统计总数+1,离线时-1
通过session监听器实现计数,但是在线人数要保存在Application域中

准备监听器

package com.lanson.listener;
import javax.servlet.ServletContext;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
/**
 * @Author: Lansonli
 * @Description: MircoMessage:Mark_7001
 */
@WebListener
public class OnLineNumberListener implements HttpSessionListener  {
    @Override
    public void sessionCreated(HttpSessionEvent se) {
        // 向application域中 增加一个数字
        HttpSession session = se.getSession();
        ServletContext application = session.getServletContext();
        Object attribute = application.getAttribute("count");
        if(null == attribute){// 第一次放数据
            application.setAttribute("count", 1);
        }else{
            int count =(int)attribute;
            application.setAttribute("count", ++count);
        }
    }
    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        // 向application域中 减少一个数字
        HttpSession session = se.getSession();
        ServletContext application = session.getServletContext();
        int count =(int)application.getAttribute("count");
        application.setAttribute("count", --count);
    }
}

准备销毁监听的servlet

package com.lanson.servlet;
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 java.io.IOException;
/**
 * @Author: Lansonli
 * @Description: MircoMessage:Mark_7001
 */
@WebServlet(urlPatterns = "/logout.do")
public class Logout extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        session.invalidate();
    }
}

index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title%sSourceCode%lt;/title>
  </head>
  <body>
  当前在线人数为:${applicationScope.count}
  </body>
</html>

分别用不同的客户端访问index.jsp 和logout.do测试即可

三、项目重启免登录

Session序列化和反序列化

1、序列化与反序列

把对象转化为字节序列的过程称为序列化（保存到硬盘，持久化）

把字节序列转化为对象的过程称为反序列化（存放于内存）

2、序列化的用途

把对象的字节序列永久保存到硬盘上，通常放到一个文件中。

把网络传输的对象通过字节序列化，方便传输本节作业

3、实现步骤

要想实现序列化和反序列化需要手动配置

3.1、新建文件如图所示：

3.2、Context.xml中文件如下

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

  <Context>

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

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

      </Manager>

  </Context>

3.3、注意实体类必须实现serializable接口

4、开发过程

4.1、准备实体类

package com.lanson.pojo;
import java.io.Serializable;
/**
 * @Author: Lansonli
 * @Description: MircoMessage:Mark_7001
 */
public class User  implements Serializable {
    private String username;
    private String pwd;

4.2、开发登录信息输入页面

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title%sSourceCode%lt;/title>
  </head>
  <body>
  <form action="loginController.do" method="post">
    用户名:<input type="text" name="user"> <br/>
    密码:<input type="password" name="pwd"><br/>
    <input type="submit" value="提交">
  </form>
  </body>
</html>

4.3、开发登录信息验证Servlet

package com.lanson.controller;
import com.lanson.listener.MySessionActivationListener;
import com.lanson.pojo.User;
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 java.io.IOException;
/**
 * @Author: Lansonli
 * @Description: MircoMessage:Mark_7001
 */
@WebServlet("/loginController.do")
public class LoginController extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("user");
        String pwd = req.getParameter("pwd");
        // user
        User user =new User(username,pwd);
        // session
        HttpSession session = req.getSession();
        session.setAttribute("user", user);
    }
}

4.4、开发校验当前是否已经登录的Controller

package com.lanson.controller;
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 java.io.IOException;
/**
 * @Author: Lansonli
 * @Description: MircoMessage:Mark_7001
 */
@WebServlet(urlPatterns = "/loginCheckController.do")
public class LoginCheckController extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 判断是否登录
        HttpSession session = req.getSession();
        Object user = session.getAttribute("user");
        Object listener = session.getAttribute("listener");// 获得对应的监听器
        String message ="";
        if(null != user){
            message="您已经登录过";
        }else{
            message="您还未登录";
        }
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=UTF-8");
        resp.getWriter().println(message);
    }
}

4.5、测试，先登录

然后请求loginCheckController.do 校验是否登录过，然后重启项目，再起请求loginCheckController.do 校验是否登录过，发现重启后，仍然是登录过的。

4.6、监听钝化和活化

准备监听器

package com.lanson.listener;
import javax.servlet.http.HttpSessionActivationListener;
import javax.servlet.http.HttpSessionEvent;
import java.io.Serializable;
/**
 * @Author: Lansonli
 * @Description: MircoMessage:Mark_7001
 */
public class MySessionActivationListener implements HttpSessionActivationListener, Serializable {
    @Override
    public void sessionWillPassivate(HttpSessionEvent se) {
        System.out.println(se.getSession().hashCode()+"即将钝化");
    }
    @Override
    public void sessionDidActivate(HttpSessionEvent se) {
        System.out.println(se.getSession().hashCode()+"已经活化");
    }
}

登录时绑定监听器

@WebServlet("/loginController.do")
public class LoginController extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("user");
        String pwd = req.getParameter("pwd");
        // user
        User user =new User(username,pwd);
        // session
        HttpSession session = req.getSession();
        session.setAttribute("user", user);
        // 绑定监听器
        session.setAttribute("listener", new MySessionActivationListener());
    }
}

重启项目，重复测试即可。

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