实验六~Web事件处理与过滤器

1. 创建一个名为exp06的Web项目，编写、部署、测试一个ServletContext事件监听器。

BookBean代码

package org.example.beans;

import java.io.Serializable;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Li_yizYa
 * Date: 2023—04—29
 * Time: 18:39
 */
@SuppressWarnings("serial")
public class BookBean implements Serializable {
    private String bookId;
    private String title;
    private String author;
    private String publisher;
    private double price;

    public String getBookId() {
        return bookId;
    }

    public void setBookId(String bookId) {
        this.bookId = bookId;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public String getPublisher() {
        return publisher;
    }

    public void setPublisher(String publisher) {
        this.publisher = publisher;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

BookDao代码

package org.example.dao;

import org.example.beans.BookBean;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Li_yizYa
 * Date: 2023—04—29
 * Time: 18:41
 */
public class BookDao {
    private static Connection c;
    public BookDao() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql://localhost:3306/web_test";
            c = DriverManager.getConnection(url, "root", "142516");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public List<BookBean> getBooks() {
        try {
            String sql = "select * from books";
            PreparedStatement ps = c.prepareStatement(sql);
            ResultSet rs = ps.executeQuery();
            List<BookBean> books = new ArrayList<>();
            while (rs.next()) {
                BookBean b = new BookBean();
                b.setBookId(rs.getString("book_id"));
                b.setAuthor(rs.getString("author"));
                b.setTitle(rs.getString("title"));
                b.setPublisher(rs.getString("publisher"));
                b.setPrice(rs.getDouble("price"));
                books.add(b);
            }
            return books;
        } catch (Exception e) {
            throw new RuntimeException("查询数据库出错", e);
        }
    }
}

【步骤1】编写监听器类MyServletContextListener.java，Web应用程序启动时创建一个数据源对象，并将其保存在ServletContext作用域中，Web应用销毁时将其清除；在ServletContext对象上添加属性、删除属性和替换属性时，在Tomcat日志中记录有关信息，包括提示信息、属性名和属性值等。

MyServletContextListener.java

package org.example.config;

import javax.servlet.*;
import java.util.Date;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Li_yizYa
 * Date: 2023—04—26
 * Time: 22:40
 */
public class MyServletContextListener implements ServletContextListener, ServletContextAttributeListener {
    private ServletContext context = null;
    @Override
    public void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) {
        context = servletContextAttributeEvent.getServletContext();
        context.log("添加属性: " + servletContextAttributeEvent.getName()
                    + ": " + servletContextAttributeEvent.getValue());
    }

    @Override
    public void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) {
        context = servletContextAttributeEvent.getServletContext();
        context.log("删除属性: " + servletContextAttributeEvent.getName()
                + ": " + servletContextAttributeEvent.getValue());
    }

    @Override
    public void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) {
        context = servletContextAttributeEvent.getServletContext();
        context.log("替换属性: " + servletContextAttributeEvent.getName()
                + ": " + servletContextAttributeEvent.getValue());
    }

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        context = servletContextEvent.getServletContext();
        context.log("应用程序已启动: " + new Date());
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        context = servletContextEvent.getServletContext();
        context.log("应用程序已销毁: " + new Date());
    }
}

【步骤2】在web.xml文件中注册监听器类。

<!DOCTYPE web-app PUBLIC
        "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
        "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
    <display-name>Archetype Created Web Application</display-name>
    <listener>
        <listener-class>org.example.config.MyServletContextListener</listener-class>
    </listener>
</web-app>

【步骤3】编写监听器测试页面：contextListenerTest.jsp：使用监听器创建的数据源对象连接是一次实验创建的MySQL数据库test，以表格的形式显示其中books数据表的所有内容。

contextListenerTest.jsp

<%@ page import="java.util.*" %>
<%@ page import="org.example.beans.*" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<jsp:useBean id="book" class="org.example.dao.BookDao" scope="session" />
<html>
<head>
    <title>contextListenerTest</title>
</head>

<body>
    <table width="500" height="256" border="1">
        <tr>
        <th scope="col">bookid</th>
        <th scope="col">title</th>
        <th scope="col">author</th>
        <th scope="col">publisher</th>
        <th scope="col">price</th>
    </tr>
    <%
        List<BookBean> bookList = book.getBooks();
        for (BookBean books : bookList) {
            String book_id = books.getBookId();
            String title = books.getTitle();
            String author = books.getAuthor();
            String publisher = books.getPublisher();
            double price = books.getPrice();
            %>
            <tr>
                <td><%=book_id%> </td>
                <td><%=title%></td>
                <td><%=author%></td>
                <td><%=publisher%></td>
                <td><%=price%></td>
            </tr>
        <% } %>
    </table>
</body>
</html>

【步骤5】检查日志文件

打开<CATALINA_HOME>\logs目录中的localhost.yyyy-mm-dd.log日志文件，查看执行事件监听器后写到日志文件中的信息。

2. 编写一个HttpSession事件监听器用来记录当前在线人数。

首先创建一个SessionBean类，用来记录sessionID和注册时间

package org.example.beans;

import java.io.Serializable;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Li_yizYa
 * Date: 2023—04—29
 * Time: 22:17
 */
@SuppressWarnings("serial")
public class SessionBean implements Serializable {
    private String id;
    private String creationTime;

    public SessionBean(String id, String creationTime) {
        this.id = id;
        this.creationTime = creationTime;
    }
    public SessionBean() {}

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getCreationTime() {
        return creationTime;
    }

    public void setCreationTime(String creationTime) {
        this.creationTime = creationTime;
    }
}

【步骤1】编写MySessionListener监听器处理类，监视Web应用会话创建事件：每创建一个新的会话对象，就将其保存到会话对象的列表数组中，并将用户会话对象列表保存在ServletContext作用域中的sessionList属性中，同时向日志中写入“创建一个新会话”以及该会话的ID。当一个会话对象被删除时，从用户会话对象列表中删除该会话对象并保存，同时向日志中写入“删除一个会话”以及该会话的ID。

package org.example.config;

import org.example.beans.SessionBean;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Li_yizYa
 * Date: 2023—04—29
 * Time: 21:59
 */
public class MySessionListener implements HttpSessionListener {
    @Override
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        ServletContext application = httpSessionEvent.getSession().getServletContext();
        List<SessionBean> sessionList = (List<SessionBean>)application.getAttribute("sessionList");
        if (sessionList == null) {
            sessionList = new ArrayList<>();
            application.setAttribute("sessionList", sessionList);
        }
        long time = httpSessionEvent.getSession().getCreationTime();
        Date date = new Date(time);
        SimpleDateFormat sd = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String creationTime = sd.format(date);
        SessionBean sessionBean = new SessionBean(httpSessionEvent.getSession().getId(),
                creationTime);
        sessionList.add(sessionBean);
        application.log("创建一个新会话，其id为: " + httpSessionEvent.getSession().getId());
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        ServletContext application = httpSessionEvent.getSession().getServletContext();
        List<SessionBean> sessionList = (List<SessionBean>)application.getAttribute("sessionList");
        String sessionId = httpSessionEvent.getSession().getId();
        for(SessionBean session : sessionList) {
            if (session.getId().equals(sessionId)) {
                sessionList.remove(session);
            }
        }
        application.log("删除一个新会话，其id为: " + sessionId);
        application.setAttribute("sessionList", sessionList);
    }
}

【步骤2】在web.xml文件中注册该事件监听器。

<!DOCTYPE web-app PUBLIC
        "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
        "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
    <display-name>Archetype Created Web Application</display-name>
    <listener>
        <listener-class>org.example.config.MyServletContextListener</listener-class>
    </listener>
    <listener>
        <listener-class>org.example.config.MySessionListener</listener-class>
    </listener>
</web-app>

【步骤3】编写一个测试该监听器的页面sessionDisplay.jsp，显示当前应用所有在线的会话对象的id及创建时间。多打开几个浏览器窗口，模拟多用户访问，查看多用户会话统计出的结果。

<%@ page import="java.util.*" %>
<%@ page import="org.example.beans.*" %>
<%@ page contentType="text/html;charset=utf-8" %>
<html>
<head>
    <title>sessionDisplay</title>
<style>
    td{
        text-align: center;
    }
</style>
</head>
<body>
    <table width="500" height="256" border="1">
        <tr>
        <th scope="col">会话id</th>
        <th scope="col">创建时间</th>
    </tr>
    <%
        ServletContext context = getServletConfig().getServletContext();
        List<SessionBean> sessionList = (List<SessionBean>) context.getAttribute("sessionList");
        for (SessionBean s : sessionList) {
            String id = s.getId();
            String creationTime = s.getCreationTime();
            %>
            <tr>
                <td><%=id%> </td>
                <td><%=creationTime%></td>
            </tr>
        <% } %>
    </table>
</body>
</html>

3. 编写一个ServletRequestListener监听器，记录某个页面自应用程序启动以来被访问的次数。

【步骤1】编写监听器接口MyRequestListener，在对指定页面onlineCount.jsp发送请求时进行该页面访问次数计数器累加，并将计数器变量保存到应用作用域的属性中。

package org.example.config;

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Li_yizYa
 * Date: 2023—04—30
 * Time: 0:04
 */
public class MyRequestListener implements ServletRequestListener {
    private int count = 0;
    @Override
    public void requestDestroyed(ServletRequestEvent servletRequestEvent) {
    }

    @Override
    public void requestInitialized(ServletRequestEvent servletRequestEvent) {
        HttpServletRequest request1 = (HttpServletRequest) servletRequestEvent.getServletRequest();
        if(request1.getRequestURI().equals("/exp06/onlineCount.jsp")){
            count++;
            servletRequestEvent.getServletContext().setAttribute("count",new Integer(count));
        }
    }
}

【步骤2】在web.xml文件中注册该监听器。

<!DOCTYPE web-app PUBLIC
        "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
        "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
    <display-name>Archetype Created Web Application</display-name>
    <listener>
        <listener-class>org.example.config.MyServletContextListener</listener-class>
    </listener>
    <listener>
        <listener-class>org.example.config.MySessionListener</listener-class>
    </listener>
    <listener>
        <listener-class>org.example.config.MyRequestListener</listener-class>
    </listener>
</web-app>

【步骤3】编写一个JSP页面onlineCount.jsp。

<%@ page contentType="text/html;charset=utf-8" language="java" %>
<html>
<head><title>Listener test</title>
</head>
<body>
欢迎您，您的IP地址是<%= request.getRemoteAddr() %>
<p>自应用程序启动以来，该页面被访问了
<font color="blue" ><%=application.getAttribute("count")%>
</font>次<br>
</body>
</html>

【步骤4】启动多个浏览器窗口访问该jsp页面，展示并分析程序的运行结果。