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实验六~Web事件处理与过滤器

news 2026/2/9 2:35:12

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;@Overridepublic void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) {context = servletContextAttributeEvent.getServletContext();context.log("添加属性: " + servletContextAttributeEvent.getName()+ ": " + servletContextAttributeEvent.getValue());}@Overridepublic void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) {context = servletContextAttributeEvent.getServletContext();context.log("删除属性: " + servletContextAttributeEvent.getName()+ ": " + servletContextAttributeEvent.getValue());}@Overridepublic void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) {context = servletContextAttributeEvent.getServletContext();context.log("替换属性: " + servletContextAttributeEvent.getName()+ ": " + servletContextAttributeEvent.getValue());}@Overridepublic void contextInitialized(ServletContextEvent servletContextEvent) {context = servletContextEvent.getServletContext();context.log("应用程序已启动: " + new Date());}@Overridepublic 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 {@Overridepublic 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());}@Overridepublic 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;@Overridepublic void requestDestroyed(ServletRequestEvent servletRequestEvent) {}@Overridepublic 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。

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