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Web---Cookie技术(显示用户上次登录的时间、显示用户最近浏览的若干个图片(按比例缩放))

本章博客讲解：
1、Cookie基本用法演示
2、演示Cookie的访问权限
3、演示Cookie的删除
4、利用Cookie显示用户上次登录的时间
5、利用Cookie技术显示用户最近浏览的若干个图片
6、测试火狐浏览器到底支持多少个Cookie和一个Cookie最大为多大

1、Cookie基本用法演示

index.jsp:

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
  </head>

  <body>
    <h1>演示Cookie技术</h1>
    <a href="CookieDemo">Cookie基本用法演示</a><br/>

  </body>
</html>

web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" 
    xmlns="http://java.sun.com/xml/ns/javaee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
    http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
  <display-name></display-name>
  <servlet>
    <servlet-name>CookieDemo</servlet-name>
    <servlet-class>cn.hncu.servlets.CookieDemo</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>CookieDemo</servlet-name>
    <url-pattern>/CookieDemo</url-pattern>
  </servlet-mapping>    
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

CookieDemo.java:

package cn.hncu.servlets;

import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.util.Random;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CookieDemo extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        //向客户端写cookie
        Random r = new Random();
        int n =r.nextInt(100);
        String name = "jack";//cookie的格式：key=value
        Cookie c = new Cookie("name", name+n);
        c.setMaxAge(60*60);//设置过期时间，以秒为单位
        c.setPath( request.getContextPath() );//该路径是:  /项目名
        //Cookie机制中，是通过path来控制权限的。只有<url-pattern>和该path相同或是它的子路径的servlet才能够访问该cookie
        //如果把一个cookie的path设为项目根目录，那么该项目下的所有servlet都能够访问它
        response.addCookie(c);

        //这一段演示cookie带中文
        String str = "我带中文";
        str  = URLEncoder.encode(str, "utf-8");//中文设置编码！！！urlencode编码
        Cookie cStr = new Cookie("str", str);
        //如果不设置setMaxAge，则浏览器一关闭就过期
        cStr.setPath("/");
        response.addCookie(cStr);

        //读取客户端发过来的cookie
        Cookie cs[] = request.getCookies();//读取cookie
        if(cs!=null){//防范一下
            for(Cookie cc:cs){
                String name2 = cc.getName();
                String val = cc.getValue();
                val = URLDecoder.decode(val, "utf-8");//原来是怎么编码的，就怎么解码！ 中文解码，ascii是原样的！
                out.print(name2+"="+val+"<br/>");
            }
        }

        out.print("Cook保存成功！");
    }

}

演示结果：

第一次点击时！session下次讲！tomcat自动生成发给客户端的！

再次进入时！
name+n–因为后面的n一直在随机生成，这个点击总是显示的是前一个的信息！

2、演示Cookie的访问权限

index.jsp:

<a href="servlet/CookieDemo2">演示Cookie的访问权限</a><br/>

web.xml:

<servlet>
    <servlet-name>CookieDemo2</servlet-name>
    <servlet-class>cn.hncu.servlets.CookieDemo2</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>CookieDemo2</servlet-name>
    <url-pattern>/servlet/CookieDemo2</url-pattern>
  </servlet-mapping>

CookieDemo2.java:

package cn.hncu.servlets;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CookieDemo2 extends HttpServlet {


    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        //向客户端写Cookie
        Random r = new Random();
        int n =r.nextInt(100);
        Cookie c = new Cookie("age", ""+n);
        c.setMaxAge(60*60);//过期时间
        c.setPath( request.getContextPath()+"/servlet/CookieDemo2" );//Cookie机制中,是通过path来控制权限的
        //由于CookieDemo的url-pattern是项目根目录/CookieDemo，不是当前cookie所设路径的子目录，因此无法访问到该cookie

        //注意！！！path不一样，那么cookie是不同的对象，也就是不会覆那个名字相同的cookie！
        response.addCookie(c);

        //读取从客户端发来的cookie
        Cookie cs[] = request.getCookies();
        if(cs!=null){
            for(Cookie cc:cs){
                String name = cc.getName();
                String val = cc.getValue();
                out.print("22222--"+name+"="+val+"<br/>");
            }
        }
        out.print("Cookie保存成功！");

    }
}

演示结果：

先进入CookieDemo2的页面，能访问到CookieDemo的name-cookie

再进入CookieDemo的页面，不能访问到CookieDemo2的age-cookie

3、演示Cookie的删除

index.jsp:

    <a href="servlet/DelCookieDemo"> 演示Cookie的删除 </a><br/>

web.xml:

<servlet>
    <servlet-name>DelCookieDemo</servlet-name>
    <servlet-class>cn.hncu.servlets.DelCookieDemo</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>DelCookieDemo</servlet-name>
    <url-pattern>/servlet/DelCookieDemo</url-pattern>
  </servlet-mapping>

DelCookieDemo.java:

package cn.hncu.servlets;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DelCookieDemo extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        Cookie cs[] = request.getCookies();
        if(cs!=null){
            for(Cookie c:cs){
        //要想遍历到"name"这个cookie，当前servlet必须要有读的权限，即servlet的url-pattern必须是该cookie所设路径或者是其所设路径的子路径
                //删除name这个cookie
                if("name".equals(c.getName())){
                    c.setPath( request.getContextPath() );//删除时是通过这一句来判断权限的！这里必须和原来所设的路径完全一样才能删除，否则不能删除！
                    //对于上句，我的个人理解是：因为如果你这个路径设置不同了，其实只是相当与新开了一个cookie，这个新cookie的到期时间是0，name是"name"

                    c.setMaxAge(0);//到期时见设为0，即是删除---此处只是设置删除标识
                    response.addCookie(c);
                }
            }
        }
    }
}

演示结果：

这个时候，name还存在的。

我们访问DelCookieDemo.

再去第一个链接看：

name已经没有了！

火狐会自动删除过期的cookie：

4、利用Cookie显示用户上次登录的时间

index.jsp:

<a href="LoginServlet">利用Cookie显示用户上次登录的时间</a>

web.xml:

 <servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>cn.hncu.servlets.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/LoginServlet</url-pattern>
  </servlet-mapping>

LoginServlet.java:

package cn.hncu.servlets;

import java.io.IOException;
import java.io.PrintWriter;
import java.text.SimpleDateFormat;
import java.util.Date;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginServlet extends HttpServlet {


    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">");
        out.println("<HTML>");
        out.println("  <HEAD><TITLE>演示利用Cookie显示用户上次登录的时间</TITLE></HEAD>");
        out.println("  <BODY>");

        //读取客户端的cookie
        Cookie cs[] = request.getCookies();
        boolean boo = false;
        if(cs!=null){
            for(Cookie c:cs){
                //遍历
                if("loginTime".equals(c.getName())){
                    String val =c.getValue();
                    long dt = Long.parseLong(val);
                    Date d = new Date(dt);
                    SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
                    out.print("您上次登录时间是："+sdf.format(d));
                    boo=true;
                    break;
                }
            }
        }
        if(boo==false){//表示之前1年没有访问记录！因为下面我们保存的过期时间是一年
            out.print("您最近一年是第一次访问。。。");
        }

        //无论是新旧用户，都会以最近的时间俩创建一个Cookie，写到客户端。原来有了的，就是更新时间
        Date d = new Date();
        Cookie c = new Cookie("loginTime", ""+d.getTime() );
        c.setPath(request.getContextPath());
        c.setMaxAge(60*60*24*30*12);
        response.addCookie(c);

        out.println("  </BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
    }

}

演示结果：

第一次访问;

再次访问：

5、利用Cookie技术显示用户最近浏览的若干个图片

index.jsp:

<a href="jsps/show.jsp">看美女--利用Cookie技术显示用户最近浏览的若干个图片</a>

web.xml:

 <servlet>
    <servlet-name>ShowServlet</servlet-name>
    <servlet-class>cn.hncu.servlets.ShowServlet</servlet-class>
  </servlet>
<servlet-mapping>
    <servlet-name>ShowServlet</servlet-name>
    <url-pattern>/showImg</url-pattern>
  </servlet-mapping>

show.jsp:

<%@page import="java.io.File"%>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <style type="text/css">
        .span{
            border:0px solid #000;
            width:100px; 
            height:100px;
            overflow:hidden;
        }
        .span img{
            max-width:100px;
            _width:expression(this.width > 100 ? "100px" : this.width);
        }
        .spans{
            border:0px solid #000;
            width:50px; 
            height:50px;
            overflow:hidden;
        }
        .spans img{
            max-width:50px;
            _width:expression(this.width > 50 ? "50px" : this.width);
        }

    </style>

  </head>

  <body>
    <h1>看美女--利用Cookie技术显示用户最近浏览的若干个图片</h1>

    <a href="/myCookieWeb/jsps/show.jsp">看美女--利用Cookie技术显示用户最近浏览的若干个图片</a>
    <h3>最近浏览的图片：</h3>

    <!-- 添加最近3次浏览的图片 -->
    <%
        String str =null;
        Cookie cs[] = request.getCookies();
        if(cs!=null){
            for(Cookie c:cs){
                if("images".equals(c.getName())){
                    str=c.getValue();// ***.jpg
                    break;
                }
            }
        }
        if(str!=null){
            String strs[] = str.split(",");
            for(String s:strs){
                %>
                    <span class="spans">
                        <img src="<%=request.getContextPath()%>/imgs/<%=s%>" />
                    </span>     
                <%
            }
        }
     %>

    <br/><hr/><br/>

    <% 
    //利用file遍历所有的图片，显示出来。
    String path = getServletContext().getRealPath("/imgs");
    //System.out.printf(path);//D:apache-tomcat-7.0.30webappsmyCookieWebjsps
    File file = new java.io.File(path);
    File[] files = file.listFiles();
    if(files!=null){
    %>

    <%
        for(File f:files){
            String imgName = f.getName();
            %>
                <span class="span">
                    <a href="<%=request.getContextPath() %>/showImg?img=<%=imgName %>">
                        <img src="<%=request.getContextPath()%>/imgs/<%=imgName%>" />
                    </a>
                </span>
            <%
        }
    %>

    <%

    }
    %>

  </body>
</html>

ShowServlet.java:

package cn.hncu.servlets;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ShowServlet extends HttpServlet {


    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">");
        out.println("<HTML>");
        out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
        out.println("  <BODY>");

        String img = request.getParameter("img");
        String imgStr = "<img src='"+request.getContextPath()+"/imgs/"+img+"'/>";
        out.print(imgStr);

        //用Cookie记录用户访问过的图片信息
        Cookie cs[] = request.getCookies();
        boolean boo = false;
        if(cs!=null){
            for(Cookie c:cs){
                if("images".equals(c.getName())){//已经有了images这个cookie
                    String imgs = c.getValue();
                    String imgStrs[] = imgs.split(",");
                    boolean booStr = false;
                    //防范点击重复的图片
                    for(int i=0;i<imgStrs.length;i++){
                        if(imgStrs[i].equals(img)){
                            if(i==1&&imgStrs.length==2){
                                imgs=imgStrs[i]+","+imgStrs[0];
                            }else if(i==2&&imgStrs.length==3){
                                imgs=imgStrs[i]+","+imgStrs[0]+","+imgStrs[1];
                            }else if(i==2&&imgStrs.length==3){
                                imgs=imgStrs[i]+","+imgStrs[0]+","+imgStrs[1];
                            }
                            booStr=true;
                            break;
                        }
                    }
                    if(!booStr){

                        imgs = img+","+imgs;//采用如下方式会麻烦一点：imgs+","+img
                        if(imgs.split(",").length>3){//如果访问的图片超过3次了
                            imgs = imgs.substring(0, imgs.lastIndexOf(","));//左包含，右不包含
                        }

                        /*//如果这样写了，最好把上面的防范重复的图片，那个添加顺序倒过来
                        //imgs+","+img  方式：
                        imgs = imgs+","+img;
                        if(imgs.split(",").length>3){//如果访问的图片超过3次了
                            imgs = imgs.substring(imgs.indexOf(",")+1, imgs.length());
                        }
                        */
                    }
                    c.setValue(imgs);//更新
                    c.setMaxAge(60*60*24*30);
                    c.setPath("/");//相当于把访问权限完全放开，即所有的项目都能访问
                    response.addCookie(c);
                    boo=true;
                    break;
                }
            }
        }
        if(boo==false){//表示首次访问，即浏览器中没有图片浏览的cookie
            Cookie c = new Cookie("images", img);
            c.setMaxAge(60*60*24*30);
            c.setPath("/");
            response.addCookie(c);
        }


        out.println("  </BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
    }

}

演示结果：

6、测试火狐浏览器到底支持多少个Cookie和一个Cookie最大为多大

index.jsp:

<a href="servlet/HowManyCookieServlet">测试火狐浏览器到底支持多少个Cookie和一个Cookie最大为多大 </a><br/>

web.xml:

 <servlet>
    <servlet-name>HowManyCookie</servlet-name>
    <servlet-class>cn.hncu.servlets.HowManyCookie</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>HowManyCookie</servlet-name>
    <url-pattern>/servlet/HowManyCookieServlet</url-pattern>
  </servlet-mapping>

HowManyCookie.java:

package cn.hncu.servlets;

import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLDecoder;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HowManyCookie extends HttpServlet {


    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        PrintWriter out = response.getWriter();

        /*
        //测试个数--火狐47.0.1 最大支持110个
        for(int i=1;i<=110;i++){
            Cookie c = new Cookie("textNum"+i, ""+i);
            c.setMaxAge(60*15);
            c.setPath("/");
            response.addCookie(c);
        }
        */

        //测试大小  ---4092字节为最大支持的单个cookie存储
        String s ="";
        for(int i=0;i<4092;i++){
            s+="1";
        }
        Cookie c = new Cookie("test", s);
        c.setMaxAge(60*15);
        c.setPath("/");
        response.addCookie(c);

        Cookie cs[] = request.getCookies();//读取cookie
        if(cs!=null){//防范一下
            for(Cookie cc:cs){
                String key = cc.getName();
                String val = cc.getValue();
                out.print(key+"="+val+" ");
            }
        }

    }

}

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原文地址：https://www.cnblogs.com/webmen/p/5739090.html