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使用Cookie实现用户商品历史浏览记录

该功能分为四个模块:

1. 获取所有商品并以链接的形式显示

1 out.write("网站商品: <br/>");
2 Map<String, Book> books = Db.getAll();
3 for (Map.Entry<String, Book> me : books.entrySet()) {
4     String id = me.getKey();
5     Book book = me.getValue();
6     out.write("<a href='/test/servlet/CookieDemo3?id="+ id +"'>"+ book.getName() +"</a><br/>");
7 }

模拟数据库和用户实体

 1 // 模拟数据库
 2 class Db {
 3 
 4     // 要求: 1有序 2查找 -> LinkedHashMap
 5     private static Map<String, Book> map = new LinkedHashMap<String, Book>();
 6 
 7     // 初始化map
 8     static {
 9         map.put("1", new Book("JavaWeb秘籍", 12.45));
10         map.put("2", new Book("Spring开发", 45.5));
11         map.put("3", new Book("SpringMVC开发", 82.45));
12         map.put("4", new Book("Mybatis开发", 75.5));
13     }
14 
15     public static Map<String, Book> getAll() {
16         return map;
17     }
18 }
19 
20 // 商品实体
21 class Book {
22 
23     private String name;
24     private double price;
25 
26     public Book(String name, double price) {
27         this.name = name;
28         this.price = price;
29     }
30 
31     public String getName() {
32         return name;
33     }
34 
35     public void setName(String name) {
36         this.name = name;
37     }
38 
39     public double getPrice() {
40         return price;
41     }
42 
43     public void setPrice(double price) {
44         this.price = price;
45     }
46 }

View Code

2. 显示用户上次浏览过的商品

通过用户携带的cookie显示用户历史浏览记录

 1 out.write("<br/>上次浏览过的商品: <br/>");
 2 Cookie[] cookies = req.getCookies();
 3 for (int i = 0; cookies != null && i < cookies.length; i++) {
 4     if (cookies[i].getName().equals("bookhistory")) {
 5         String bookhistoryValue = cookies[i].getValue();  // 1_4_3
 6         String[] ids = bookhistoryValue.split("\_");  // [1, 4, 3]
 7         // 迭代浏览过的商品id
 8         for (String id : ids) {
 9             out.write(Db.getAll().get(id).getName() + "<br/>");
10         }
11     }
12 }

说明: 第一步和第二步可以做成同一个servlet中, 完整代码:

 1 /**
 2  * Created by IntelliJ IDEA.
 3  *
 4  * @Auther: ShaoHsiung
 5  * @Date: 2018/8/28 10:12
 6  * @Title: 显示用户上次浏览商品
 7  * @Description: 主页
 8  */
 9 public class CookieDemo2 extends HttpServlet {
10     @Override
11     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
12 
13         // 设置浏览器编码
14         resp.setContentType("text/html; charset=utf-8");
15 
16         Writer out = resp.getWriter();
17 
18         // 获取所有商品并以链接的形式显示
19         out.write("网站商品: <br/>");
20         Map<String, Book> books = Db.getAll();
21         for (Map.Entry<String, Book> me : books.entrySet()) {
22             String id = me.getKey();
23             Book book = me.getValue();
24             out.write("<a href='/test/servlet/CookieDemo3?id="+ id +"'>"+ book.getName() +"</a><br/>");
25         }
26 
27         // 显示用户上次浏览过的商品
28         out.write("<br/>上次浏览过的商品: <br/>");
29         Cookie[] cookies = req.getCookies();
30         for (int i = 0; cookies != null && i < cookies.length; i++) {
31             if (cookies[i].getName().equals("bookhistory")) {
32                 String bookhistoryValue = cookies[i].getValue();  // 1_4_3
33                 String[] ids = bookhistoryValue.split("\_");  // [1, 4, 3]
34                 // 迭代浏览过的商品id
35                 for (String id : ids) {
36                     out.write(Db.getAll().get(id).getName() + "<br/>");
37                 }
38             }
39         }
40     }
41 
42     @Override
43     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
44         doGet(req, resp);
45     }
46 }
47 
48 // 模拟数据库
49 class Db {
50 
51     // 要求: 1有序 2查找 -> LinkedHashMap
52     private static Map<String, Book> map = new LinkedHashMap<String, Book>();
53 
54     // 初始化map
55     static {
56         map.put("1", new Book("JavaWeb秘籍", 12.45));
57         map.put("2", new Book("Spring开发", 45.5));
58         map.put("3", new Book("SpringMVC开发", 82.45));
59         map.put("4", new Book("Mybatis开发", 75.5));
60     }
61 
62     public static Map<String, Book> getAll() {
63         return map;
64     }
65 }
66 
67 // 商品实体
68 class Book {
69 
70     private String name;
71     private double price;
72 
73     public Book(String name, double price) {
74         this.name = name;
75         this.price = price;
76     }
77 
78     public String getName() {
79         return name;
80     }
81 
82     public void setName(String name) {
83         this.name = name;
84     }
85 
86     public double getPrice() {
87         return price;
88     }
89 
90     public void setPrice(double price) {
91         this.price = price;
92     }
93 }

View Code

3. 显示商品详细信息

通过请求参数在数据库中查询商品

1 out.write("商品详细信息: <br/>");
2 String id = req.getParameter("id");
3 Book book = Db.getAll().get(id);
4 out.write(book.getName() + "<br/>");
5 out.write(book.getPrice() + "<br/>");

4. 将商品的id添加到cookie中并返回给用户

这里使用makeCookie()方法封装商品历史记录cookie的制作, 这部分主要任务就是将cookie返回给浏览器

1 String bookhistoryValue = makeCookie(req, id);
2 Cookie bookhistory = new Cookie("bookhistory", bookhistoryValue);
3 bookhistory.setMaxAge(3600);
4 bookhistory.setPath(this.getServletContext().getContextPath());
5 resp.addCookie(bookhistory);

5. 完成makeCookie()方法

使用字符串拼接的方式产生cookie的具体步骤, 特别需要注意四种可能获取到的cookie及其处理方式.

注意: 四种可能获取到的cookie:

获取到的cookie    查看商品   返回的cookie
   null            1          1
   1_2_3           4        4_1_2
   1_2_3           2        2_1_3
   1_2             4        1_2_4

 1 private String makeCookie(HttpServletRequest req, String id) {
 2     String bookhistoryValue = null;
 3     Cookie[] cookies = req.getCookies();
 4     for (int i = 0; cookies != null && i < cookies.length; i++) {
 5         if (cookies[i].getName().equals("bookhistory")) {
 6             bookhistoryValue = cookies[i].getValue();
 7         }
 8     }
 9 
10     // null            1          1
11     if (bookhistoryValue == null) {
12         return id;
13     }
14     List l = Arrays.asList(bookhistoryValue.split("\_"));
15     // 转化为链表方便操作, 提供addFirst和removeLast等方法
16     LinkedList<String> list = new LinkedList();
17     list.addAll(l);
18     if (list.contains(id)) {
19         // 1_2_3           2        2_1_3
20         list.remove(id);
21         list.addFirst(id);
22     } else {
23         // 1_2_3           4        4_1_2
24         if (list.size() == 3) {
25             list.removeLast();
26             list.addFirst(id);
27         } else {
28             // 1_2             4        1_2_4
29             list.addFirst(id);
30         }
31     }
32     StringBuffer buffer = new StringBuffer();
33     for (String newId : list) {
34         buffer.append(newId + "_");  // 1_5_3_
35     }
36     return buffer.deleteCharAt(buffer.length()-1).toString();  // 删除最后一个下划线
37 }

说明: 同理, 第三步和第四步可以做成同一个servlet中, 完整代码:

 1 /**
 2  * Created by IntelliJ IDEA.
 3  *
 4  * @Auther: ShaoHsiung
 5  * @Date: 2018/8/28 10:12
 6  * @Title: 显示用户上次浏览商品
 7  * @Description: 商品详细信息页面
 8  */
 9 public class CookieDemo3 extends HttpServlet {
10     @Override
11     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
12 
13         resp.setContentType("text/html; charset=utf-8");
14 
15         Writer out = resp.getWriter();
16 
17         // 显示商品详细信息
18         out.write("商品详细信息: <br/>");
19         String id = req.getParameter("id");
20         Book book = Db.getAll().get(id);
21         out.write(book.getName() + "<br/>");
22         out.write(book.getPrice() + "<br/>");
23 
24         // 将商品的id添加到cookie中并返回给用户
25         String bookhistoryValue = makeCookie(req, id);
26         Cookie bookhistory = new Cookie("bookhistory", bookhistoryValue);
27         bookhistory.setMaxAge(3600);
28         bookhistory.setPath(this.getServletContext().getContextPath());
29         resp.addCookie(bookhistory);
30     }
31 
32     private String makeCookie(HttpServletRequest req, String id) {
33 
34         String bookhistoryValue = null;
35 
36         Cookie[] cookies = req.getCookies();
37         for (int i = 0; cookies != null && i < cookies.length; i++) {
38             if (cookies[i].getName().equals("bookhistory")) {
39                 bookhistoryValue = cookies[i].getValue();
40             }
41         }
42 
43         /*
44             重点: 四种情况
45 
46          获取到的cookie    查看商品   返回的cookie
47             null            1          1
48             1_2_3           4        4_1_2
49             1_2_3           2        2_1_3
50             1_2             4        1_2_4
51          */
52 
53         // null            1          1
54         if (bookhistoryValue == null) {
55             return id;
56         }
57 
58 
59         List l = Arrays.asList(bookhistoryValue.split("\_"));
60         // 转化为链表方便操作, 提供addFirst和removeLast等方法
61         LinkedList<String> list = new LinkedList();
62         list.addAll(l);
63         if (list.contains(id)) {
64             // 1_2_3           2        2_1_3
65             list.remove(id);
66             list.addFirst(id);
67         } else {
68             // 1_2_3           4        4_1_2
69             if (list.size() == 3) {
70                 list.removeLast();
71                 list.addFirst(id);
72             } else {
73                 // 1_2             4        1_2_4
74                 list.addFirst(id);
75             }
76         }
77 
78         StringBuffer buffer = new StringBuffer();
79         for (String newId : list) {
80             buffer.append(newId + "_");  // 1_5_3_
81         }
82 
83         return buffer.deleteCharAt(buffer.length()-1).toString();  // 删除最后一个下划线
84     }
85 
86     @Override
87     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
88         doGet(req, resp);
89     }
90 }

View Code

效果图:

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原文地址：https://www.cnblogs.com/shaohsiung/p/9546995.html