Day40

Day40

监听器

概念：
监听器用于监听web应用中某些对象信息的创建、销毁、增加，修改，删除等动作的
发生，然后作出相应的响应处理。当范围对象的状态发生变化的时候，服务器自动调用
监听器对象中的方法。
常用于统计在线人数和在线用户，系统加载时进行信息初始化，统计网站的访问量等。

类别：

第一大类：监听请求域、会话域、全局域对象的创建和销毁。

第二大类：监听请求域、会话域、全局域对象的属性的创建、替换、销毁。

第三大类：监听会话域（String key - Object value）里value的绑定和解绑、钝化和活化。

第一大类

监听请求域：

servlet：

package com.qf.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 java.io.IOException;
@WebServlet("/Servlet01")
public class Servlet01 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request, response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("执行Servlet");}
}

web.xml:

<listener><listener-class>com.qf.listen.MyServletRequestListener</listener-class></listener>

listener:

package com.qf.listen;import javax.servlet.ServletRequest;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;public class MyServletRequestListener implements ServletRequestListener {@Overridepublic void requestDestroyed(ServletRequestEvent servletRequestEvent) {ServletRequest request = servletRequestEvent.getServletRequest();System.out.println("请求对象被销毁了"+request);}@Overridepublic void requestInitialized(ServletRequestEvent servletRequestEvent) {ServletRequest request = servletRequestEvent.getServletRequest();System.out.println("请求对象被创建了"+request);}
}

注：请求对象的生命周期为，创建：客户端发送请求，服务器会创建请求对象。销毁：服务器返回响应后，会把请求对象、响应对象一并销毁。

监听会话域

注意：查看生命周期要把index.jsp改名或者删除，因为项目启动会默认进入index.jsp，会创建会话对象。

web.xml:（手动调整session销毁时间）

<listener><listener-class>com.qf.listen.MyHttpSessionListener</listener-class></listener><session-config><session-timeout>1</session-timeout></session-config>

创建一个page01.jsp。

MyHttpSessionListener:

package com.qf.listen;import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;public class MyHttpSessionListener implements HttpSessionListener {@Overridepublic void sessionCreated(HttpSessionEvent httpSessionEvent) {HttpSession session = httpSessionEvent.getSession();System.out.println("会话对象被创建了"+session.getId());}@Overridepublic void sessionDestroyed(HttpSessionEvent httpSessionEvent) {System.out.println("会话对象被销毁了");}
}

注：会话对象的什么周期，创建：服务器使用到了session->request.getSession();销毁：session对象设置的过期时间到后就会被销毁。

思考1：客户端访问html资源是否会创建会话对象？答：不会

思考2：客户端访问jsp资源会创建会话对象？为什么？答：会，因为jsp里9大内置对象中有session对象。

思考3：session对象创建后，客户端发送下一次请求是为什么能找到之前的session对象？答：因为客户端在cookie中存储了session的id->JSESSIONID

思考4：session对象是存活在服务器中的，默认为30分钟的生命周期，可客户端存储的cookie里的JSESSIONID为会话结束时，也就意味着关闭浏览器后，再也找不到之前存储在服务器中的session对象，那怎么解决？

答：设置cookie中JSESSION的过期时间。

package com.qf.servlet;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;
@WebServlet("/Servlet01")
public class Servlet01 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request, response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("Servlet收到请求");HttpSession session = request.getSession();Cookie cookie = new Cookie("JSESSION",session.getId());cookie.setMaxAge(60*30);response.addCookie(cookie);response.getWriter().println("abc");}
}

监听全局域

web.xml:

<context-param><param-name>info</param-name><param-value>abc</param-value></context-param><listener><listener-class>com.qf.listen.MyServletContextListener</listener-class></listener>

MyServletContextListener:

package com.qf.listen;import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;public class MyServletContextListener implements ServletContextListener {@Overridepublic void contextInitialized(ServletContextEvent servletContextEvent) {ServletContext servletContext = servletContextEvent.getServletContext();String info = servletContext.getInitParameter("info");System.out.println("全局对象被创建了"+"--"+info);}@Overridepublic void contextDestroyed(ServletContextEvent servletContextEvent) {System.out.println("全局对象被销毁了");}
}

注：1.生命周期为项目启动时创建，服务器正常关闭时销毁。

经验：应用场景：

监听全局域对象的创建和销毁，而全局域对象在项目启动时创建，就意味着监听器里的初始化方法在项目启动时就会被调用，所以我们可以把项目初始化的工作放在该方法里。在配置文件中context-param里设置初始数据（建议放在最上面），在监听器的初始化方法中可以用getInitParameter（）方法获取数据。

第一大类使用案例-统计在线人数

在全局域监听器中创建：

        servletContext.setAttribute("count",0);

在会话域监听器中统计：

package com.qf.listen;import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;public class MyHttpSessionListener implements HttpSessionListener {@Overridepublic void sessionCreated(HttpSessionEvent httpSessionEvent) {HttpSession session = httpSessionEvent.getSession();System.out.println("会话对象被创建了"+session.getId());ServletContext servletContext = session.getServletContext();int count = (int) servletContext.getAttribute("count");count++;servletContext.setAttribute("count",count);}@Overridepublic void sessionDestroyed(HttpSessionEvent httpSessionEvent) {System.out.println("会话对象被销毁了");HttpSession session = httpSessionEvent.getSession();ServletContext servletContext = session.getServletContext();int count = (int) servletContext.getAttribute("count");count--;servletContext.setAttribute("count",count);}
}

第二大类

请求属性监听器

MyServletRequestAttributeListener（用注解配置）:

package com.qf.listen02;import javax.servlet.ServletRequestAttributeEvent;
import javax.servlet.ServletRequestAttributeListener;
import javax.servlet.annotation.WebListener;@WebListener
public class MyServletRequestAttributeListener implements ServletRequestAttributeListener {@Overridepublic void attributeAdded(ServletRequestAttributeEvent servletRequestAttributeEvent) {String name = servletRequestAttributeEvent.getName();Object value = servletRequestAttributeEvent.getValue();System.out.println("请求域对象添加了属性："+name+"---"+value);}@Overridepublic void attributeRemoved(ServletRequestAttributeEvent servletRequestAttributeEvent) {String name = servletRequestAttributeEvent.getName();Object value = servletRequestAttributeEvent.getValue();System.out.println("请求域对象删除了属性："+name+"---"+value);}@Overridepublic void attributeReplaced(ServletRequestAttributeEvent servletRequestAttributeEvent) {String name = servletRequestAttributeEvent.getName();Object value = servletRequestAttributeEvent.getValue();//获取被替换的值System.out.println("请求域对象替换了属性："+name+"---"+value);}
}

page.jsp:

<%//操作请求域的属性request.setAttribute("msg","aaabbbccc");//添加属性request.setAttribute("msg","bbbcccddd");//替换属性request.removeAttribute("msg");//删除属性
%>

会话属性监听器

MyHttpSessionAttributeListener:

package com.qf.listen02;import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;public class MyHttpSessionAttributeListener implements HttpSessionAttributeListener {@Overridepublic void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {String name = httpSessionBindingEvent.getName();Object value = httpSessionBindingEvent.getValue();System.out.println("会话域对象添加了属性");}@Overridepublic void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {String name = httpSessionBindingEvent.getName();Object value = httpSessionBindingEvent.getValue();System.out.println("会话域对象删除了属性");}@Overridepublic void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {String name = httpSessionBindingEvent.getName();Object value = httpSessionBindingEvent.getValue();System.out.println("会话域对象替换了属性");}
}

page02.jsp:

<%//操作会话域的属性session.setAttribute("msg","aaabbbccc");//添加属性session.setAttribute("msg","bbbcccddd");//替换属性session.removeAttribute("msg");//删除属性
%>

全局属性监听器

MyServletContextAttributeListener:

package com.qf.listen02;import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;public class MyServletContextAttributeListener implements ServletContextAttributeListener {@Overridepublic void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) {String name = servletContextAttributeEvent.getName();Object value = servletContextAttributeEvent.getValue();System.out.println("全局对象创建了属性："+"--"+name+"--"+value);}@Overridepublic void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) {String name = servletContextAttributeEvent.getName();Object value = servletContextAttributeEvent.getValue();System.out.println("全局对象创建了属性："+"--"+name+"--"+value);}@Overridepublic void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) {String name = servletContextAttributeEvent.getName();Object value = servletContextAttributeEvent.getValue();System.out.println("全局对象创建了属性："+"--"+name+"--"+value);}
}

page03.jsp:

<%//操作全局域的属性application.setAttribute("msg","aaabbbccc");//添加属性application.setAttribute("msg","bbbcccddd");//替换属性application.removeAttribute("msg");//删除属性
%>

第三大类

HttpSessionBindingListener：监听JavaBean对象在session中的绑定（添加）和解绑（删除）,即监听某一个具体的类对象，第二大类是监听所有的类对象。

HttpSessionActivationListener:监听JavaBean对象在session中的钝化（序列化）和活化（反序列化）

User:（实现HttpSessionBindingListener，HttpSessionActivationListener，Serializable）

package com.qf.listen03;import javax.servlet.http.HttpSessionActivationListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
import javax.servlet.http.HttpSessionEvent;
import java.io.Serializable;public class User implements HttpSessionBindingListener, HttpSessionActivationListener, Serializable {private String username;private String password;private String name;private String nickName;public User(String username, String password, String name, String nickName) {this.username = username;this.password = password;this.name = name;this.nickName = nickName;}public User() {}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getNickName() {return nickName;}public void setNickName(String nickName) {this.nickName = nickName;}@Overridepublic String toString() {return "User{" +"username='" + username + '\'' +", password='" + password + '\'' +", name='" + name + '\'' +", nickName='" + nickName + '\'' +'}';}@Overridepublic void sessionWillPassivate(HttpSessionEvent httpSessionEvent) {System.out.println(this+"被session钝化了");}@Overridepublic void sessionDidActivate(HttpSessionEvent httpSessionEvent) {System.out.println(this+"被session活化了");}@Overridepublic void valueBound(HttpSessionBindingEvent httpSessionBindingEvent) {System.out.println(this+"绑定到session中了");}@Overridepublic void valueUnbound(HttpSessionBindingEvent httpSessionBindingEvent) {System.out.println(this+"从session中解绑了");}
}

在web里面创建META-INF文件夹，写一个context.xml:

<?xml version="1.0" encoding="UTF-8"?>
<Context><Manager className="org.apache.catalina.session.PersistentManager" maxIdleSwap="1"><Store className="org.apache.catalina.session.FileStore" directory="C:\\text"/></Manager>
</Context>

Servlet02:

package com.qf.servlet;import com.qf.listen03.User;import javax.servlet.ServletException;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
@WebServlet("/Servlet02")
public class Servlet02 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request, response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("Servlet02接收到请求了...");HttpSession session = request.getSession();//注意：将user对象添加到session中，可以叫做User对象绑定到session中 --- 绑定session.setAttribute("user",new User("1233211234567","123132","zs","fwkt"));//注意：将user对象从session中删除，可以叫做User对象从session中解绑了 --- 解绑session.removeAttribute("user");}
}

Servlet03:

package com.qf.servlet;import com.qf.listen03.User;import javax.servlet.ServletException;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;@WebServlet("/Servlet03")
public class Servlet03 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request, response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("Servlet03接收到请求了...");HttpSession session = request.getSession();session.setAttribute("user",new User("1233211234567","123132","zs","fwkt"));}
}

注意：将User对象添加到session中，可以叫做User对象绑定到session中 — 绑定

将User对象从session中删除，可以叫做User对象从session中解绑 — 解绑

面试题：session的钝化与活化：

过滤器

简介

Filter：过滤器，拦截访问web资源的请求与响应操作

Servlet API中提供了Filter接口，开发web应用时，如果编写的Java类实现了这个接口，则把这个Java类称之为过滤器。

创建与使用

场景：welcome.html向Servlet01发送请求：

package com.qf.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 java.io.IOException;
@WebServlet("/Servlet01.action")
public class Servlet01 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request, response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.setCharacterEncoding("UTF-8");response.setContentType("text/html;charset=UTF-8");System.out.println("Servlet收到请求了");}
}

过滤器：

package com.qf.filter;import javax.servlet.*;
import java.io.IOException;public class Filter01 implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {System.out.println("Filter01 --- init()");}@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("Filter01 --- doFilter() -- 放行前");filterChain.doFilter(servletRequest,servletResponse);System.out.println("Filter01 --- doFilter() -- 放行后");}@Overridepublic void destroy() {System.out.println("Filter01 --- destroy()");}
}

配置文件：

<welcome-file-list><welcome-file>welcome.html</welcome-file></welcome-file-list><filter><filter-name>Filter01</filter-name><filter-class>com.qf.filter.Filter01</filter-class></filter><filter-mapping><filter-name>Filter01</filter-name><url-pattern>*.action</url-pattern></filter-mapping>

生命周期

创建：项目启动时创建 – 构造方法、init（）

销毁：项目正常关闭时销毁 – destroy（）

注意：Filter对象是单例的。

当有多个过滤器时，

配置文件：

<filter><filter-name>Filter01</filter-name><filter-class>com.qf.filter.Filter01</filter-class></filter><filter-mapping><filter-name>Filter01</filter-name><url-pattern>*.action</url-pattern></filter-mapping><filter><filter-name>Filter02</filter-name><filter-class>com.qf.filter.Filter01</filter-class></filter><filter-mapping><filter-name>Filter02</filter-name><url-pattern>*.action</url-pattern></filter-mapping><filter><filter-name>Filter03</filter-name><filter-class>com.qf.filter.Filter01</filter-class></filter><filter-mapping><filter-name>Filter03</filter-name><url-pattern>*.action</url-pattern></filter-mapping>

思考：多个Filter的创建顺序？多个Filter调用顺序？

创建顺序：无序，底层是多线程抢资源。调用顺序为web.xml里的配置顺序（推荐）。如果是使用注解配置，是按照类名字典排序。

案例1 编码过滤器

WEB-学生管理系统中写一个Encoderfilter类进行编码过滤（就不必在servlet中设置了）

配置文件（标准写法要求匹配所有的action，但是由于之前项目中servlet后没有加.action，故此处偷懒直接写/*）：

<welcome-file-list><welcome-file>welcome.html</welcome-file></welcome-file-list><filter><filter-name>EncoderFilter</filter-name><filter-class>com.qf.filter.EncoderFilter</filter-class></filter><filter-mapping><filter-name>EncoderFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping>

过滤器：

package com.qf.filter;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;public class EncoderFilter implements Filter {private String code;@Overridepublic void init(FilterConfig filterConfig) throws ServletException {code = filterConfig.getInitParameter("code");}@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) servletRequest;HttpServletResponse response = (HttpServletResponse) servletResponse;request.setCharacterEncoding(code);response.setContentType("text/html;charset="+code);filterChain.doFilter(request,response);}@Overridepublic void destroy() {}
}

案例2 登录权限过滤器

写一个LoginFilter。

配置文件：

<filter><filter-name>LoginFilter</filter-name><filter-class>com.qf.filter.LoginFilter</filter-class></filter><filter-mapping><filter-name>LoginFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping>

LoginFilter:

package com.qf.filter;import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;public class LoginFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) servletRequest;HttpServletResponse response = (HttpServletResponse) servletResponse;String requestURI = request.getRequestURI();System.out.println(requestURI);
//        StringBuffer requestURL = request.getRequestURL();
//        System.out.println(requestURL);HttpSession session = request.getSession();String username = (String) session.getAttribute("username");String role = (String) session.getAttribute("role");String name = (String) session.getAttribute("name");if(requestURI.equals("/Day37_war_exploded/register.jsp")||requestURI.equals("/Day37_war_exploded/login.jsp")||requestURI.equals("/Day37_war_exploded/CodeServlet")||requestURI.equals("/Day37_war_exploded/LoginServlet")||requestURI.equals("/Day37_war_exploded/")||requestURI.equals("/Day37_war_exploded/welcome.html")){filterChain.doFilter(request,response);}else{if(username!=null&&role!=null&&name!=null){if("student".equals(role) && requestURI.contains("QueryAllStuServlet")) {response.sendRedirect("index.jsp");}else{filterChain.doFilter(request,response);}}}}@Overridepublic void destroy() {}
}

案例3 敏感词过滤器

场景：在学生详情页面写一个建议，跳转到proposal.jsp，里面写一个表单，提交到ProposalServlet

<%--Created by IntelliJ IDEA.User: GuDate: 2024-06-17Time: 17:37To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head><title>Title</title>
</head>
<body><h2>建议</h2><form action="ProposalServlet" method="post">建议：<input type="text" name="proposal"/><input type="submit" value="提交"/><button type="button" οnclick="fun01()">返回</button></form><script type="text/javascript">function fun01(){window.location = "index.jsp";}</script>
</body>
</html>

ProposalServlet(输出建议)：

package com.qf.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 java.io.IOException;
@WebServlet("/ProposalServlet")
public class ProposalServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request, response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String proposal = (String) request.getParameter("proposal");response.getWriter().println(proposal);}
}

MyHttpServletRequestWrapper包装类，继承HttpServletRequestWrapper类（构造方法、重写getParameter方法）：

package com.qf.pojo;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;public class MyHttpServletRequestWrapper extends HttpServletRequestWrapper {public MyHttpServletRequestWrapper(HttpServletRequest request) {super(request);}@Overridepublic String getParameter(String name) {String parameter = super.getParameter(name);if(parameter!=null){parameter = parameter.replaceAll("<","&lt;");parameter = parameter.replaceAll(">","&gt;");parameter = parameter.replaceAll("傻逼","**");}return parameter;}
}

SensitiveWordsFilter:

package com.qf.filter;import com.qf.pojo.MyHttpServletRequestWrapper;import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;public class SensitiveWordFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) servletRequest;MyHttpServletRequestWrapper requestWrapper = new MyHttpServletRequestWrapper(request);filterChain.doFilter(requestWrapper,servletResponse);}@Overridepublic void destroy() {}
}