一诡右、實驗內(nèi)容

1、Filter的理解和應(yīng)用

實現(xiàn)一個禁止緩存的過濾器轻猖。

要求和提示：

（1）禁止瀏覽器緩存所有動態(tài)頁面帆吻；

（2）有3個http響應(yīng)頭字段可以禁止瀏覽器緩存當前頁面，它們在Servlet中的示例代碼如下咙边。

response.setDateHeader("Expires",-1);

response.setHeader("Cache-Control","no-cache");

response.setHeader("Pragma","no-cache");

（3）并不是所有的瀏覽器都能完全支持上面的3個響應(yīng)頭猜煮，因此最好是同時使用上面的3個響應(yīng)頭次员。

代碼如下：
ExampleFilter.java

package com.qst.chapter02;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebFilter("/ExampleFilter")
public class ExampleFilter implements Filter {


    public ExampleFilter() {
        // TODO Auto-generated constructor stub
    }


    public void destroy() {
        // TODO Auto-generated method stub
    }

     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
              
            //HttpServletRequest req=(HttpServletRequest) request;  
            HttpServletResponse res=(HttpServletResponse) response;  
       
            res.setDateHeader("Expires",-1);
            res.setHeader("Cache-Control","no-cache");
            res.setHeader("Pragma","no-cache");
            chain.doFilter(request, response);
            
        }
    public void init(FilterConfig fConfig) throws ServletException {
        // TODO Auto-generated method stub
    }

}

xml配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" id="WebApp_ID" version="4.0">
  <display-name>chapter02</display-name>

<filter>
    <filter-name>ExampleFilter</filter-name>
    <filter-class>com.qst.chapter02.ExampleFilter</filter-class>
  </filter>
  
  <filter-mapping>
    <filter-name>ExampleFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
</web-app>

驗證方法：打開一個瀏覽器（不能在編譯器自帶的瀏覽器中打開），在網(wǎng)頁中右鍵點審查元素王带，network中找到頁面淑蔚，如下圖

image.png

image.png

image.png

2、Filter的理解和應(yīng)用

設(shè)計一個簡單的IP地址過濾器愕撰，根據(jù)用戶的IP地址進行網(wǎng)站的訪問控制刹衫。例如：禁止IP地址處在192.168.2網(wǎng)段的用戶對網(wǎng)站的訪問。
思路：
用字符串模擬一個IP地址搞挣，通過過濾器带迟，觀察是否能打開網(wǎng)頁,網(wǎng)頁代碼隨便一個皆可。
代碼：
ExampleFilter.java

package com.qst.chapter02;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.ws.Response;

@WebFilter("/ExampleFilter")
public class ExampleFilter implements Filter {

    private String ip;
    private String[] ips;
    public ExampleFilter() {
        // TODO Auto-generated constructor stub
    }


    public void destroy() {
        // TODO Auto-generated method stub
    }

     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
              
            HttpServletRequest req=(HttpServletRequest) request;  
            HttpServletResponse res=(HttpServletResponse) response;  
            //模擬IP地址
            String localip="192.168.2.50";
            //拆分字符,提取部分IP地址
            String localipnum=localip.substring(0,localip.lastIndexOf("."));
            if(localipnum.equals("192.168.2"))
            {
                response.getWriter().print("IP："+localip);
                response.getWriter().print("error!");
            }
            else
            {
                chain.doFilter(request, response);
            }

            
        }
    public void init(FilterConfig fConfig) throws ServletException {
        // TODO Auto-generated method stub
    }

}

效果：
模擬地址192.168.2.50

image.png

image.png

3囱桨、Listener的理解和應(yīng)用

通過監(jiān)聽器記錄在線用戶的姓名仓犬，在頁面進行用戶姓名的顯示，同時實現(xiàn)對某個用戶的強制下線功能舍肠。
思路：
用監(jiān)聽器監(jiān)聽每一次會話的發(fā)起和結(jié)束搀继，然后將信息保存下來并顯示，注意翠语，因為每一次的session會話都是要由不同的客戶端發(fā)起的叽躯，所以你在運行的時候是無法在同一個瀏覽器測試的，請在多個瀏覽器打開網(wǎng)頁地址同時測試啡专，或者將瀏覽器關(guān)閉再重新打開一個新的會話（但這樣的話你就無法關(guān)閉上一次會話創(chuàng)建的用戶）险毁，退出也是只能退出你此次session會話創(chuàng)建的用戶。強制下線功能需要在退出代碼中查找想要退出用戶的sessionID们童，然后將其移除map即可畔况，下面的代碼沒有該功能，可以在此代碼基礎(chǔ)上更改慧库。
代碼：
監(jiān)聽器OnlineLoginUserViewListener.java代碼

package com.qst.chapter02;

import java.util.Date;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;


/**
 * Application Lifecycle Listener implementation class OnlineLoginUserViewListener
 *
 */
@WebListener
public class OnlineLoginUserViewListener implements HttpSessionAttributeListener {

    /**
     * Default constructor. 
     */
    public OnlineLoginUserViewListener() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpSessionAttributeListener#attributeAdded(HttpSessionBindingEvent)
     */
    @SuppressWarnings("unchecked")
    public void attributeAdded(HttpSessionBindingEvent arg0)  { 
        HttpSession session = arg0.getSession();
        //獲取表示用戶成功登陸后的會話域?qū)傩評sername
        String username = (String) session.getAttribute("username");
        if (username != null) {
            
            //將登陸的用戶信息封裝到j(luò)avabean中
            UserSessionInfo userSessionBean = new UserSessionInfo(username,session.getId(), new Date(session.getCreationTime()));
            
            //map表
            Map<String, UserSessionInfo> onlineRegister = (Map<String, UserSessionInfo>) session.getServletContext().getAttribute("onlineRegister");
            if (onlineRegister == null) {
                
                onlineRegister = new HashMap<String, UserSessionInfo>();
            }
            
            //將登錄信息保存到map中跷跪，key為sessionId
            onlineRegister.put(session.getId(), userSessionBean);
            
            //保存更新后的登陸用戶信息
            session.getServletContext().setAttribute("onlineRegister",onlineRegister);
        }
    }

    /**
     * 刪除session時
     */
    public void attributeRemoved(HttpSessionBindingEvent arg0)  { 
         // TODO Auto-generated method stub
        if ("username".equals(arg0.getName())) {
            HttpSession session = arg0.getSession();
            
            Map<String, UserSessionInfo> onlineRegister = (Map<String, UserSessionInfo>) session
                    .getServletContext().getAttribute("onlineRegister");     
            onlineRegister.remove(session.getId());   
            session.getServletContext().setAttribute("onlineRegister",
                    onlineRegister);
        }
    }

    /**
     * @see HttpSessionAttributeListener#attributeReplaced(HttpSessionBindingEvent)
     */
    public void attributeReplaced(HttpSessionBindingEvent arg0)  { 
         // TODO Auto-generated method stub
    }
    
}

用戶信息javabean,UserSessionInfo.java

package com.qst.chapter02;

import java.io.IOException;
import java.util.Date;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class UserSessionInfo {

    private String username;
    
    private String sessionID;
    
    private Date creationDate;
    
    public UserSessionInfo(){
        
    }

    public UserSessionInfo(String username, String sessionID, Date creationDate) {
        super();
        this.username = username;
        this.sessionID = sessionID;
        this.creationDate = creationDate;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getSessionID() {
        return sessionID;
    }

    public void setSessionID(String sessionID) {
        this.sessionID = sessionID;
    }

    public Date getCreationDate() {
        return creationDate;
    }

    public void setCreationDate(Date creationDate) {
        this.creationDate = creationDate;
    }

}

實時在線用戶顯示頁面onlineLoginUserView.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>view</title>
</head>
<body>
<c:forEach items="${applicationScope.onlineRegister}" var="mapRegister">
        <p>
            用戶名：${mapRegister.value.username}，會話創(chuàng)建時間：
            <fmt:formatDate value="${mapRegister.value.creationDate}"
                pattern="yyyy-MM-dd HH:mm:ss" /> 
                <a href="logoutPro.jsp">退出</a>            
        </p>
    </c:forEach>
    <a href="loginPro.jsp">注冊登錄</a>      
</body>
</html>

登陸頁面longinPro.jsp

<%@page import="java.util.Random"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>用戶登錄</title>
</head>
<body>
    <%
    session.setAttribute("username","用戶1"+new Random().nextInt());
    //System.out.print("用戶"+new Random().nextInt());
    response.sendRedirect("onlineLoginUserView.jsp");
    %>
    
</body>
</html>

退出頁面logoutPro.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>用戶退出</title>
</head>
<body>
    <p>已經(jīng)退出本系統(tǒng)齐板！</p> 
    
    <%
    //String username =  request.getParameter("username");
    //System.out.print(username);
    session.removeAttribute("username");
    response.sendRedirect("onlineLoginUserView.jsp");
    %>
    
</body>
</html>

運行效果：
未有用戶注冊時

image.png

image.png

image.png

總結(jié)

下面是廢話甘磨，可不看橡羞。。济舆。卿泽。
過濾器和監(jiān)聽器是java web中非常重要的兩個功能，可以幫助我們處理很多邏輯上的問題滋觉，通過監(jiān)聽器監(jiān)聽網(wǎng)頁發(fā)出的請求签夭，就可以及時的對請求進行處理齐邦，通過過濾器過濾掉我們不需要的信息，可以大大提高網(wǎng)頁運行的效率第租，也方便程序員對頁面操作進行編程措拇。