使用Cookie實現用戶商品歷史瀏覽記錄

該功能分爲四個模塊:

1. 獲取全部商品並以連接的形式顯示

1 out.write("網站商品: <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 }

模擬數據庫和用戶實體

 1 // 模擬數據庫
 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祕籍", 12.45)); 10         map.put("2", new Book("Spring開發", 45.5)); 11         map.put("3", new Book("SpringMVC開發", 82.45)); 12         map.put("4", new Book("Mybatis開發", 75.5)); 13  } 14 
15     public static Map<String, Book> getAll() { 16         return map; 17  } 18 } 19 
20 // 商品實體
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 }

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2. 顯示用戶上次瀏覽過的商品

經過用戶攜帶的cookie顯示用戶歷史瀏覽記錄

 1 out.write("<br/>上次瀏覽過的商品: <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         // 迭代瀏覽過的商品id
 8         for (String id : ids) {  9             out.write(Db.getAll().get(id).getName() + "<br/>"); 10  } 11  } 12 }

說明: 第一步和第二步能夠作成同一個servlet中, 完整代碼:

 1 /**
 2  * Created by IntelliJ IDEA.  3  *  4  * @Auther: ShaoHsiung  5  * @Date: 2018/8/28 10:12  6  * @Title: 顯示用戶上次瀏覽商品  7  * @Description: 主頁  8  */
 9 public class CookieDemo2 extends HttpServlet { 10  @Override 11     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 12 
13         // 設置瀏覽器編碼
14         resp.setContentType("text/html; charset=utf-8"); 15 
16         Writer out = resp.getWriter(); 17 
18         // 獲取全部商品並以連接的形式顯示
19         out.write("網站商品: <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         // 顯示用戶上次瀏覽過的商品
28         out.write("<br/>上次瀏覽過的商品: <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                 // 迭代瀏覽過的商品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 // 模擬數據庫
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祕籍", 12.45)); 57         map.put("2", new Book("Spring開發", 45.5)); 58         map.put("3", new Book("SpringMVC開發", 82.45)); 59         map.put("4", new Book("Mybatis開發", 75.5)); 60  } 61 
62     public static Map<String, Book> getAll() { 63         return map; 64  } 65 } 66 
67 // 商品實體
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 }

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3. 顯示商品詳細信息

經過請求參數在數據庫中查詢商品

1 out.write("商品詳細信息: <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. 將商品的id添加到cookie中並返回給用戶

這裏使用makeCookie()方法封裝商品歷史記錄cookie的製做, 這部分主要任務就是將cookie返回給瀏覽器

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產生cookie的具體步驟, 特別須要注意四種可能獲取到的cookie及其處理方式.

注意: 四種可能獲取到的cookie:

獲取到的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     // 轉化爲鏈表方便操做, 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();  // 刪除最後一個下劃線
37 }

說明: 同理, 第三步和第四步能夠作成同一個servlet中, 完整代碼:

 1 /**
 2  * Created by IntelliJ IDEA.  3  *  4  * @Auther: ShaoHsiung  5  * @Date: 2018/8/28 10:12  6  * @Title: 顯示用戶上次瀏覽商品  7  * @Description: 商品詳細信息頁面  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         // 顯示商品詳細信息
18         out.write("商品詳細信息: <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         // 將商品的id添加到cookie中並返回給用戶
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  重點: 四種狀況 45 
46  獲取到的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         // 轉化爲鏈表方便操做, 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();  // 刪除最後一個下劃線
84  } 85 
86  @Override 87     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 88  doGet(req, resp); 89  } 90 }

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效果圖: