【JSP開發】利用cookie實現商品瀏覽記錄

在主頁中顯示商品，點擊商品可以查看商品的具體信息，帶用戶瀏覽完之後，回到主頁，就會看到自己曾經瀏覽過什麼商品。


商品主頁Servlet

CookieDemo3.java:
package cn.edu.cookie;


import java.io.IOException;
import java.io.PrintWriter;
import java.util.LinkedHashMap;
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;
//代表首頁的Servlet
public class CookieDemo3 extends HttpServlet {


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

        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out=response.getWriter();

       //1.輸出網站所有商品
        out.write("本網站有如下商品：<br/>");
        Map<String,Book> map = Db.getAll();
        for(Map.Entry<String, Book> entry :map.entrySet())
        {
            Book book=entry.getValue();
            out.print("<a href='/day07/CookieDemo4?id="+book.getId()+"' terget='_blank'>"+book.getName()+"</a><br/>");
        }

       //2.輸出用戶曾經看過的商品
        out.print("您曾經看過如下商品：<br/>");
        Cookie cookies[]= request.getCookies();
        for(int i=0;cookies!=null&&i<cookies.length;i++)
        {
            //是不是要加if(cookies[i].getName().equals("BookHistory"))判斷？
            String ids[]=cookies[i].getValue().split("\\,");
            for(String id:ids){
                Book book=(Book)Db.getAll().get(id);
                out.print(book.getName()+"<br/>");
            }

        }
    }


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


}


//如果有檢索數據的需求，用雙列（Map）的容器，若沒有用單列的（List）
//模擬數據庫
class Db{
    private static Map<String,Book> map=new LinkedHashMap();//HashMap取出來和存進去的順序不是一致的（自己測試）
    //類初始化代碼（寫在靜態代碼塊裏）
    static{
        map.put("1",new Book("1","JAVAWEB開發","老張","一本好書！"));
        map.put("2",new Book("2","JDBC開發","老張","一本好書！"));
        map.put("3",new Book("3","Spring開發","老黎","一本好書！"));
        map.put("4",new Book("4","struts開發","老畢","一本好書！"));
        map.put("5",new Book("5","android開發","老黎","一本好書！"));
    }

    public static Map getAll(){
        return map;
    }
}


class Book{
    private String id;
    private String name;
    private String author;
    private String description;

    public Book(){
        super();
    }
    public Book(String id, String name, String author, String description) {
        super();
        this.id = id;
        this.name = name;
        this.author = author;
        this.description = description;
    }
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getAuthor() {
        return author;
    }
    public void setAuthor(String author) {
        this.author = author;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }


}

CookieDemo4.java是每件商品的詳細信息Servlet，在這裏，cookie中的"BookHistory"就是存儲的瀏覽記錄，記錄的是
瀏覽每件商品的id記錄順序的字符串。組建該字符串的時候需要注意一下四種情況:
1.當一件商品都沒有瀏覽過時，即BookHistory=null 
此時加入的商品直接組成字符串CookieValue即可，假設此時瀏覽過id=1的商品，
CookieValue="1";

2.當瀏覽的商品是以前瀏覽過的，即BookHistory="2,5,1"的時候此時又瀏覽了id=1的

商品，這個時候，就要找到原來的那個id，刪除它，將此次瀏覽的記錄加入到最前面。

即BookHistory="2,5,1"變成了BookHistory="1,2,5"

3.由於我們的商品瀏覽記錄有限，只記錄前三個，所以每當新的記錄加入的時候，要判斷
是否滿三個，滿了的話，刪除最後一個，將最新的加入到最前面。
如BookHistory=2,5,4，當又瀏覽了1商品，要改成BookHistory=1,2,5

4.如果不滿3個，又不和以前的重複，直接將記錄加在最前面即可
如BookHistory=2,5的時候，又瀏覽了1商品，此時BookHistory=1,2,5

CookieDemo4.java

[java] view plain copy

package cn.edu.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;
//顯示商品詳細信息的Servlet
public class CookieDemo4 extends HttpServlet {


    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out=response.getWriter();

        //根據用戶帶過來的id，顯示相應商品的詳細信息
        //getParameter是拿到客戶機帶過來的數據(通過表單和鏈接傳遞的參數使用getParameter)
        String id =request.getParameter("id");//當兩個Web組件之間爲轉發關係時採用getAttribute
        Book book=(Book) Db.getAll().get(id);


        out.write(book.getId()+"<br/>");
        out.write(book.getAuthor()+"<br/>");
        out.write(book.getName()+"<br/>");
        out.write(book.getDescription()+"<br/>");

        //構建cookie，回寫給瀏覽器

        /*一個web應用最多能被瀏覽器記錄20個左右的cookie
                           所以這裏要把大量的cookie記錄到一起，記錄成一個cookie*/
        String CookieValue =buildCookie(id,request);
        Cookie cookie=new Cookie("BookHistory",CookieValue);
        cookie.setMaxAge(1*30*24*3600);
        cookie.setPath("/day07");
        response.addCookie(cookie);
    }


    private String buildCookie(String id, HttpServletRequest request) {

        //四種cookie情況
        //BookHistory=null   1   1
        //BookHistory=2,5,1   1   1,2,5
        //BookHistory=2,5,4   1   1,2,5
        //BookHistory=2,5   1   1,2,5

        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){
            return id;
        }

        //分割成數組，之後將數組轉成集合,集合轉成鏈表
        LinkedList<String> list=new LinkedList(Arrays.asList(BookHistory.split("\\,")));
        //分情況分配新的cookie值
        if(list.contains(id)){
            //BookHistory=2,5,1   1   1,2,5
            list.remove(id);
            list.addFirst(id);
        }else{
            if(list.size()>=3){
                //BookHistory=2,5,4   1   1,2,5
                list.removeLast();
                list.addFirst(id);
            }else{
                //BookHistory=2,5   1   1,2,5
                //BookHistory=null   1   1
                list.addFirst(id);
            }
        }

        StringBuffer sb=new StringBuffer();
        for(String bid : list){
            sb.append(bid+",");
        }

        return sb.deleteCharAt(sb.length()-1).toString();
    }


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


}