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

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

模拟数据库和用户实体

 // 模拟数据库
 class Db {

     // 要求: 1有序 2查找 -> LinkedHashMap
     private static Map<String, Book> map = new LinkedHashMap<String, Book>();

     // 初始化map
     static {
         map.put("1", new Book("JavaWeb秘籍", 12.45));
         map.put("2", new Book("Spring开发", 45.5));
         map.put("3", new Book("SpringMVC开发", 82.45));
         map.put("4", new Book("Mybatis开发", 75.5));
     }

     public static Map<String, Book> getAll() {
         return map;
     }
 }

 // 商品实体
 class Book {

     private String name;
     private double price;

     public Book(String name, double price) {
         this.name = name;
         this.price = price;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public double getPrice() {
         return price;
     }

     public void setPrice(double price) {
         this.price = price;
     }
 }

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

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

说明: 第一步和第二步可以做成同一个servlet中, 完整代码:

 /**
  * Created by IntelliJ IDEA.
  *
  * @Auther: ShaoHsiung
  * @Date: 2018/8/28 10:12
  * @Title: 显示用户上次浏览商品
  * @Description: 主页
  */
 public class CookieDemo2 extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         // 设置浏览器编码
         resp.setContentType("text/html; charset=utf-8");

         Writer out = resp.getWriter();

         // 获取所有商品并以链接的形式显示
         out.write("网站商品: <br/>");
         Map<String, Book> books = Db.getAll();
         for (Map.Entry<String, Book> me : books.entrySet()) {
             String id = me.getKey();
             Book book = me.getValue();
             out.write("<a href='/test/servlet/CookieDemo3?id="+ id +"'>"+ book.getName() +"</a><br/>");
         }

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

     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         doGet(req, resp);
     }
 }

 // 模拟数据库
 class Db {

     // 要求: 1有序 2查找 -> LinkedHashMap
     private static Map<String, Book> map = new LinkedHashMap<String, Book>();

     // 初始化map
     static {
         map.put("1", new Book("JavaWeb秘籍", 12.45));
         map.put("2", new Book("Spring开发", 45.5));
         map.put("3", new Book("SpringMVC开发", 82.45));
         map.put("4", new Book("Mybatis开发", 75.5));
     }

     public static Map<String, Book> getAll() {
         return map;
     }
 }

 // 商品实体
 class Book {

     private String name;
     private double price;

     public Book(String name, double price) {
         this.name = name;
         this.price = price;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public double getPrice() {
         return price;
     }

     public void setPrice(double price) {
         this.price = price;
     }
 }

3. 显示商品详细信息

通过请求参数在数据库中查询商品

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

 String bookhistoryValue = makeCookie(req, id);
 Cookie bookhistory = new Cookie("bookhistory", bookhistoryValue);
 bookhistory.setMaxAge(3600);
 bookhistory.setPath(this.getServletContext().getContextPath());
 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

 private String makeCookie(HttpServletRequest req, String id) {
     String bookhistoryValue = null;
     Cookie[] cookies = req.getCookies();
     for (int i = 0; cookies != null && i < cookies.length; i++) {
         if (cookies[i].getName().equals("bookhistory")) {
             bookhistoryValue = cookies[i].getValue();
         }
     }

     // null            1          1
     if (bookhistoryValue == null) {
         return id;
     }
     List l = Arrays.asList(bookhistoryValue.split("\\_"));
     // 转化为链表方便操作, 提供addFirst和removeLast等方法
     LinkedList<String> list = new LinkedList();
     list.addAll(l);
     if (list.contains(id)) {
         // 1_2_3           2        2_1_3
         list.remove(id);
         list.addFirst(id);
     } else {
         // 1_2_3           4        4_1_2
         if (list.size() == 3) {
             list.removeLast();
             list.addFirst(id);
         } else {
             // 1_2             4        1_2_4
             list.addFirst(id);
         }
     }
     StringBuffer buffer = new StringBuffer();
     for (String newId : list) {
         buffer.append(newId + "_");  // 1_5_3_
     }
     return buffer.deleteCharAt(buffer.length()-1).toString();  // 删除最后一个下划线
 }

说明: 同理, 第三步和第四步可以做成同一个servlet中, 完整代码:

 /**
  * Created by IntelliJ IDEA.
  *
  * @Auther: ShaoHsiung
  * @Date: 2018/8/28 10:12
  * @Title: 显示用户上次浏览商品
  * @Description: 商品详细信息页面
  */
 public class CookieDemo3 extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         resp.setContentType("text/html; charset=utf-8");

         Writer out = resp.getWriter();

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

         // 将商品的id添加到cookie中并返回给用户
         String bookhistoryValue = makeCookie(req, id);
         Cookie bookhistory = new Cookie("bookhistory", bookhistoryValue);
         bookhistory.setMaxAge(3600);
         bookhistory.setPath(this.getServletContext().getContextPath());
         resp.addCookie(bookhistory);
     }

     private String makeCookie(HttpServletRequest req, String id) {

         String bookhistoryValue = null;

         Cookie[] cookies = req.getCookies();
         for (int i = 0; cookies != null && i < cookies.length; i++) {
             if (cookies[i].getName().equals("bookhistory")) {
                 bookhistoryValue = cookies[i].getValue();
             }
         }

         /*
             重点: 四种情况

          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
          */

         // null            1          1
         if (bookhistoryValue == null) {
             return id;
         }

         List l = Arrays.asList(bookhistoryValue.split("\\_"));
         // 转化为链表方便操作, 提供addFirst和removeLast等方法
         LinkedList<String> list = new LinkedList();
         list.addAll(l);
         if (list.contains(id)) {
             // 1_2_3           2        2_1_3
             list.remove(id);
             list.addFirst(id);
         } else {
             // 1_2_3           4        4_1_2
             if (list.size() == 3) {
                 list.removeLast();
                 list.addFirst(id);
             } else {
                 // 1_2             4        1_2_4
                 list.addFirst(id);
             }
         }

         StringBuffer buffer = new StringBuffer();
         for (String newId : list) {
             buffer.append(newId + "_");  // 1_5_3_
         }

         return buffer.deleteCharAt(buffer.length()-1).toString();  // 删除最后一个下划线
     }

     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         doGet(req, resp);
     }
 }

效果图: