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Java Cookie技术 详细学习Java Cookie技术(用户登录、浏览、访问权限)

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本章文章详细讲解：
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-7.0.30\webapps\myCookieWeb\jsps
 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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