利用Cookie，实现动态显示用户曾经浏览过的商品

1、在DisPlay的servlet中主要做两件事情

     1.1显示在出售的商品

     1.2显示顾客曾经浏览的商品

DisPlay的代码如下：

package com.baowei.cookie;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

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 Display extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        
        doPost(req, resp);
    }
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        
        //显示所有的图书
        PrintWriter  out = resp.getWriter();
        out.print("本书店出售的图书如下:<br/>");
        
        Map<String,Book> books = DB.getDBMap();
        Set<Entry<String, Book>> set = books.entrySet();
        Iterator<Entry<String, Book>>  it = set.iterator();
        while(it.hasNext()){
            Entry<String, Book> entry = it.next();
            Book book = entry.getValue();
            out.print("<a href='/HuiHuaTest/BookDetail?id="+book.getId()+"' target='_blank'>"+book.getName()+"</a><br/>");
                
        }
        
        //用户最近看过的图书
        out.print("你最近浏览过的图书如下:<br/>");
        Cookie cookie = null;
        Cookie [] cookies = req.getCookies();
        for (int   i = 0; cookies != null &&   i < cookies.length;   i++) { 
            if(cookies[i].getName().equals("bookHistory")){
                cookie = cookies[i];
            }
        }
        
        if(cookie!=null){
            //找到了bookHistory这个cookie
            String bookHistory = cookie.getValue();   //4_6_1
            String ids[] = bookHistory.split("\_"); //这样划分更好
            for(String id: ids){
                Book book = (Book) DB.getDBMap().get(id);
                out.print(book.getName() + "<br/>");
            }
        }
        
    }

}

2. 对于图书的详细介绍的BookDetail的servlet，也是两个功能

   2.1 介绍商品的详细信息

   2.2 将浏览过的商品的信息加入到Cookie中，并且将Cookie写回浏览器

BookDetail的实现代码如下：

 1 package com.baowei.cookie;
 2 
 3 import java.io.IOException;
 4 import java.io.PrintWriter;
 5 import java.util.Arrays;
 6 import java.util.LinkedList;
 7 
 8 import javax.servlet.ServletException;
 9 import javax.servlet.http.Cookie;
10 import javax.servlet.http.HttpServlet;
11 import javax.servlet.http.HttpServletRequest;
12 import javax.servlet.http.HttpServletResponse;
13 
14 public class BookDetail extends HttpServlet {
15 
16     public void doGet(HttpServletRequest request, HttpServletResponse response)
17             throws ServletException, IOException {
18 
19         doPost(request, response);
20 
21     }
22 
23     public void doPost(HttpServletRequest request, HttpServletResponse response)
24             throws ServletException, IOException {
25 
26         response.setContentType("text/html;charset=UTF-8");
27         response.setCharacterEncoding("UTF-8");
28         PrintWriter out = response.getWriter();
29 
30         // 1.根据用户带过来的id值，显示相应商品的信息
31         out.print("您想看的书的详细信息为：<br/>");
32         String id = request.getParameter("id");
33         Book book = (Book) DB.getDBMap().get(id);
34         out.print(book.getId() + "<br/>");
35         out.print(book.getName() + "<br/>");
36         out.print(book.getAuthor() + "<br/>");
37 
38         // 2.以cookie的形式回写该商品的id号给浏览器
39         String bookHistory = makeCookie(book.getId(), request);
40         Cookie cookie = new Cookie("bookHistory", bookHistory);
41         //cookie.setMaxAge(10000); //将Cookie保存在硬盘内
42         response.addCookie(cookie);
43 
44     }
45 
46     // 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
47     private String makeCookie(String id, HttpServletRequest request) {
48 
49         // bookHistory=null    3   bookHistory=3
50         // bookHistory=2_1_5   3   bookHistory=3_2_1
51         // bookHistory=2 3     3   bookHistory=3_2
52         // bookHistory=2_3     3   bookHistory=3_2
53 
54         // 1.得到用户曾经看过的书
55         String bookHistory = null;
56         Cookie cookies[] = request.getCookies();
57         for (int i = 0; cookies != null && i < cookies.length; i++) {
58             if (cookies[i].getName().equals("bookHistory")) {
59                 bookHistory = cookies[i].getValue();
60             }
61         }
62 
63         if (bookHistory == null) {
64             bookHistory = id;
65             return bookHistory;
66         }
67 
68         // 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
69         String ids[] = bookHistory.split("_");
70         // 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
71         LinkedList<String> idList = new LinkedList(Arrays.asList(ids));
72     
73         if (idList.contains(id)) {
74             idList.remove(id);
75         } else {
76             if (idList.size() >= 5) {
77                 idList.removeLast();
78             }
79         }
80         idList.addFirst(id);
81 
82         StringBuffer sb = new StringBuffer();
83         for (String lid : idList) { // 1_2_3_
84             sb.append(lid + "_");
85         }
86 
87         return sb.deleteCharAt(sb.length() - 1).toString();
88     }
89 
90 }

上面两个程序中用到的Book类和DB类如下：

Book类的代码：

 1 package com.baowei.cookie;
 2 
 3 public class Book {
 4     
 5     private String id;
 6     private String name;
 7     private String author;
 8     
 9     public Book() {
10 
11     }
12     
13     public Book(String id, String name, String author) {
14         this.id = id;
15         this.name = name;
16         this.author = author;
17     }
18     public String getId() {
19         return id;
20     }
21     public void setId(String id) {
22         this.id = id;
23     }
24     public String getName() {
25         return name;
26     }
27     public void setName(String name) {
28         this.name = name;
29     }
30     public String getAuthor() {
31         return author;
32     }
33     public void setAuthor(String author) {
34         this.author = author;
35     }
36     
37     
38 
39 }

DB类的代码如下：

package com.baowei.cookie;

import java.util.HashMap;
import java.util.Map;

public class DB {
    
    static Map<String,Book>   map = new HashMap<String,Book>();
    
    static {
        
        map.put("1", new Book("1","JavaWeb开发","张保卫") );
        map.put("2", new Book("2","操作系统","张保卫") );
        map.put("3", new Book("3","Spring开发","张保卫") );
        map.put("4", new Book("4","Struts2开发","张保卫") );
        map.put("5", new Book("5","Java基础开发","张保卫") );
        map.put("6", new Book("6","数据结构","张保卫") );
        map.put("7", new Book("7","ACM","张保卫") );
        map.put("8", new Book("8","计算机网络","张保卫") );
        map.put("9", new Book("9","软件工程","张保卫") );
        map.put("10", new Book("10","Android开发","张保卫") );    
    }
    
    public static Map<String,Book> getDBMap(){ 
        return map;   
    }
   
}
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原文地址：https://www.cnblogs.com/zhangbaowei/p/4676577.html