Session用法案例 -->實作簡單購物車功能(實際項目可能不會這麼使用)

07120170909

1、session是在cookie的基礎之上，利用cookie傳回JSESSIONID(key[伺服器随機生成])存在用戶端實作，正真的資料存在服務端[key-value]。

2、session的使用步驟：

1)、設定：request.getSession().setAttribute("username", username);

2)、擷取：request.getSession(false).getAttribute(username); 注：[false表示沿用之前設定的；不設定，預設為true，如果存在session，則沿用之前的，沒有則建立];

3、session是每個浏覽器對應一個JSESSIONID;   --->注：例如設定session之後，在Resquest Headers 會存在Cookie:JSESSIONID=A75D52D01876F3B404B8CC668BC8180C

4、代碼如下：

package com.tiger.two0906.bean;

import java.io.*;
import java.util.*;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;

/**
 * 水果儲存到購物車
 * @author tiger
 * @time 2017年9月9日
 */
@WebServlet("/fruitSave")
public class FruitSave extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    public FruitSave() { }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List
   
     fruit_list = (List
    
     ) request.getServletContext().getAttribute("fruit_list");
        String[] ids = request.getParameterValues("sg");
        List
     
       fruits = new ArrayList<>();
        for (Fruit fruit : fruit_list) {
            Integer id = fruit.getId();
            for (String d : ids) {
                if (id==Integer.parseInt(d)) {
                    fruits.add(fruit);
                }
            }
        }
        //将資訊添加到session中，不同的客戶擁有不同的水果清單
        request.getSession().setAttribute("fruits", fruits);
        response.sendRedirect("shopCar");
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}
package com.tiger.two0906.bean;

import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;

@WebServlet("/shopCar")
public class FruitCar extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
        List
      
        fruits =  (List
       
        ) request.getSession().getAttribute("fruits"); PrintWriter out = response.getWriter(); out.println(""); out.println(""); out.println("
        ");
        out.println("---shopCar---");
        out.println(""); out.println(""); out.println(""); out.println("
        
         "); for (Fruit fruit : fruits) { out.println( "
         
           " + "
           "+fruit.getId()+"" + "
           "+fruit.getName()+"" + "
           "+fruit.getPrice()+"" + "
           "+fruit.getCount() +"" + "
          "); } out.println("
         
        "); out.println(""); out.println(""); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } } package com.tiger.two0906.bean; /** * 水果bean * @author tiger * @time 2017年9月6日 */ public class Fruit { Integer id; String name; double price; int count; public void setId(Integer id) { this.id = id; } public Integer getId() { return id; } 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; } public int getCount() { return count; } public void setCount(int count) { this.count = count; } public Fruit() { } public Fruit(Integer id, String name, double price, int count) { super(); this.id = id; this.name = name; this.price = price; this.count = count; } @Override public String toString() { return "Fruits [id=" + id + ", name=" + name + ", price=" + price + ", count=" + count + "]"; } } package com.tiger.two0906.bean; import java.io.*; import java.util.*; import javax.servlet.*; import javax.servlet.annotation.WebServlet; import javax.servlet.http.*; /** * 07120170909 * 水果清單 * @author tiger * @time 2017年9月6日 */ @WebServlet("/shopList") public class FruitList extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); response.setCharacterEncoding("UTF-8"); response.setContentType("text/html;charset=UTF-8"); //資料源 Fruit[] fruits = {new Fruit(1,"蘋果",2.32, 22), new Fruit(2,"雪梨",2.32, 22), new Fruit(3,"堅果",2.32, 22), new Fruit(4,"蘋果",2.32, 22), new Fruit(5,"葡萄",2.32, 22)}; //将資料源添加進List集合 List
        
          fruit_list = new ArrayList
         
          (); Collections.addAll(fruit_list, fruits); request.getServletContext().setAttribute("fruit_list", fruit_list); PrintWriter out = response.getWriter(); out.println(""); out.println(""); out.println("
          ");
        out.println("---shopList---");
        out.println(""); out.println(""); out.println(""); out.println("      

​​");
        out.println("
     ");
        out.println("
     
       ");
        out.println("
       選擇");
        out.println("
       水果名");
        out.println("
       價格");
        out.println("
       數量");
        out.println("
      ");
        for (Fruit fruit : fruit_list) {
            out.println( "
      
"
                            + "
       "+fruit.getName()+""
                            + "
       "+fruit.getPrice()+""
                            + "
       "+fruit.getCount() +"" );
        }
        out.println("
      
       ");
        out.println("
       ");
        out.println("");
        out.println("
       ");
        out.println("
      
      ");
        out.println("
     
    ");
        out.println("");
        out.println("");
    }
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        doPost(req, resp);
    }
}
​​