Cookie小案例------记住浏览过的商品记录

          我们知道，这个功能在电商项目中很常见。这里处理请求和页面显示都是由servlet实现，主要是为了体现cookie的作用，

实现功能如下：

1，点击购买的商品后，显示到另一页面

2，记住用户浏览过的商品，并在页面时中显示

3，当浏览过的数量超过最大值限度时，最下面一个商品被挤下去

4，当浏览过的商品本身就在浏览记录中，显示列表将其从中间移到最上面

显示一打开网站的样子和显示用户的浏览记录：

package cn.itcast.cookie;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//网站首页
public class CookieDemo2 extends HttpServlet {

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

		response.setContentType("text/html;charset=UTF-8");
		response.setCharacterEncoding("UTF-8");
		PrintWriter  out = response.getWriter();
		
		//1.显示网站所有商品
		out.print("本网站有如下书籍：<br/>");
		Map<String,Book> map = DB.getMap();
		for(Map.Entry<String, Book> entry : map.entrySet()){
			Book book = entry.getValue();
			out.print("<a href=http://www.mamicode.com/'/day07/servlet/CookieDemo3?id="+book.getId()+"' target='_blank'>"+book.getName()+"
");>


用于显示商品的详细信息：
package cn.itcast.cookie;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.LinkedList;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//显示商品详细信息
public class CookieDemo3 extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html;charset=UTF-8");
		response.setCharacterEncoding("UTF-8");
		PrintWriter  out = response.getWriter();
		
		//1.根据用户带过来的id值，显示相应商品的信息
		out.print("您想看的书的详细信息为：<br/>");
		String id = request.getParameter("id");
		Book book = (Book) DB.getMap().get(id);
		out.print(book.getId() + "<br/>");
		out.print(book.getName() + "<br/>");
		out.print(book.getAuthor() + "<br/>");
		
		
		//2.以cookie的形式回写该商品的id号给浏览器
		String bookHistory = makeCookie(book.getId(),request);
		Cookie cookie = new Cookie("bookHistory",bookHistory);
		cookie.setMaxAge(10000);
		response.addCookie(cookie);
		
	}

	//根据用户原来看过的书，以及现在看的书的id，构建新的cookie值
	private String makeCookie(String id, HttpServletRequest request) {
		
		//bookHistory=null    3     bookHistory=3
		//bookHistory=2_1_5   3     bookHistory=3_2_1
		//bookHistory=2       3     bookHistory=3_2
		//bookHistory=2_3     3     bookHistory=3_2
		
		
		//1.得到用户曾经看过的书
		String bookHistory = null;
		Cookie cookies[] = request.getCookies();
		for(int i=0;cookies!=null && i<cookies.length;i++){
			if(cookies[i].getName().equals("bookHistory")){
				bookHistory = cookies[i].getValue();
			}
		}
		
		if(bookHistory==null){
			bookHistory = id;
			return bookHistory;
		}

		//bookHistory=1_2_5    代表用户曾经看一些书，接着程序要得到用户曾经看过什么书
		String ids[] = bookHistory.split("_");
		//为了检测数组中是否包含当前id，我们应该把数据转成集合，并且还要转成链表结构的集合
		LinkedList<String> idList = new LinkedList(Arrays.asList(ids));
		/*if(idList.contains(id)){
			//bookHistory=2_3     3     bookHistory=3_2
			idList.remove(id);
			idList.addFirst(id);
		}else{
			//bookHistory=2_1_5   3     bookHistory=3_2_1
			if(idList.size()>=3){
				idList.removeLast();
				idList.addFirst(id);
			}else{
				//bookHistory=2       3     bookHistory=3_2
				idList.addFirst(id);
			}
		}*/
		if(idList.contains(id)){
			idList.remove(id);
		}else{
			if(idList.size()>=3){
				idList.removeLast();
			}
		}
		idList.addFirst(id);
		
		StringBuffer sb = new StringBuffer();
		for(String lid: idList){   //1_2_3_
			sb.append(lid + "_");
		}
		
		return sb.deleteCharAt(sb.length()-1).toString();
	}

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

}



运行效果：


Cookie小案例-----记住浏览过的商品记录