Dynamic website conversation and painting technology

1. Session Overview

Goal: Understand the concept of sessions and be able to know what sessions are used for

In daily life, a series of questions and answers between making a call and hanging up the phone is a conversation. During the phone call, both parties will have conversation content. Similarly, during the interaction between the client and the server, some data will also be generated. For example, users A and B have logged into the shopping website respectively. A purchased an iPhone and B purchased an iPad. When these two users check out, the web server needs to save the information of users A and B respectively.为了保存会话过程中产生的数据，Servlet提供了两个用于保存会话数据的对象，分别是Cookie和Session。

2. Cookie case demonstration - displaying the user’s last visit time

1. Create a Web project

• Web Project -CookieDemo
  
  

2. Modify the Artifact name and redeploy the project

Modify the Artifact name in the project structure window

• Edit the server configuration, redeploy the project, and the URL becomes http://localhost:8080/CookieDemo/
• Modify homepage
• Start the server and see the effect
  

3. Create the LastAccessServlet class

Create the net.xyx.servlet package, and then create the LastAccessServlet class inside

package net.xyx.servlet;

import jdk.nashorn.internal.ir.CallNode;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.text.SimpleDateFormat;
import java.util.Date;

@WebServlet(name = "LastAccessServlet", value = "/LastAccessServlet")
public class LastAccessServlet extends javax.servlet.http.HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置响应对象内容类型（网页、编码），避免中文乱码
        response.setContentType("text/html; charset=utf-8");
        //打印输出流
        PrintWriter out = response.getWriter();
        //获取所有cookie
        Cookie[] cookies = request.getCookies();
        //定义标志变量isFirstAccess
        boolean isFirsetAccess = true;
        //判断cookies是否为空
        if (cookies.length > 0 && cookies != null){
            //遍历cookies数组
            for (Cookie cookie : cookies){
                //获取cookie的名称
                String name = cookie.getName();
                //判断cookie名称是否为“lastTime”
                if (name.equals("lastTime")){
                    //用户不是第一次访问
                    isFirsetAccess = false;
                    //获取cookie的值（上次访问时间）
                    String value = cookie.getValue();
                    //控制台输出解码的数据
                    System.out.println("解码前：" + value);
                    //对cookie值进行URL解码
                    value = URLDecoder.decode(value,"utf-8");
                    //控制台输出解码后的数据
                    System.out.println("解码后" + value);
                    //在页面显示用户上次访问时间
                    out.print("欢迎回来，您上次访问时间" + value);
                    //获取当前时间字符串，重新设置cookie
                    Date date = new Date();
                    SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
                    String strDate = sdf.format(date);
                    //控制台输出编码前的日期数据
                    System.out.println("编码前：" + strDate);
                    //对日期数据进行URL编码
                    strDate = URLEncoder.encode(strDate,"utf-8");
                    //控制台输出编码后的日期数据
                    System.out.println("编码后：" + strDate);
                    //设置cookie的值
                    cookie.setValue(strDate);
                    //设置cookie的存储时间（以秒为单位）
                    cookie.setMaxAge(30*24*60*60);//一个月
                    //加入cookie，让其生效
                    response.addCookie(cookie);
                }
            }
        }if (isFirsetAccess){//cookie为空，表明是第一次访问
            //获取当前时间字符串，重新设置cookie
            Date date = new Date();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
            String strDate = sdf.format(date);
            //控制台输出编码前的日期数据
            System.out.println("编码前：" + strDate);
            //对日期数据进行URL编码
            strDate = URLEncoder.encode(strDate,"utf-8");
            //控制台输出编码后的日期数据
            System.out.println("编码后：" + strDate);
            //创建一个cookie
            Cookie cookie = new Cookie("lastTime", strDate);
            //设置cookie的值
            cookie.setValue(strDate);
            //设置cookie的存储时间（以秒为单位）
            cookie.setMaxAge(30*24*60*60);//一个月
            //加入cookie，让其生效
            response.addCookie(cookie);
            //在页面显示欢迎用户首次访问信息
            out.print("您好，欢迎您首次访问本网站~");
        }
    }

    protected void doGet(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)
            throws javax.servlet.ServletException, IOException {
        doPost(request,response);

    }
}

3. Session case demonstration - implementing shopping cart

Goal: Use Session-related knowledge to implement the function of simulated shopping cart

1. Create a cake entity class

• Create SessionDemo project
  
  

• Edit homepage
  

• Create the net.xyx.session.bean package, and then create the Cake class in the package
  

package net.xyx.session.bean;

public class Cake {
    private  String id;
    private String name;

    public Cake(){

    }

    public Cake(String id, String name){
        this.id = id;
        this.name = name;
    }

    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;
    }
}

2. Create cake data access object

package net.xyx.session.dao;

import net.xyx.session.bean.Cake;

import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.Map;

public class CakeDao {
    private static Map<String, Cake> cakes = new LinkedHashMap<>();

    static {
        cakes.put("1",new Cake ("1","A类蛋糕"));
        cakes.put("2",new Cake ("2","B类蛋糕"));
        cakes.put("3",new Cake ("3","C类蛋糕"));
        cakes.put("4",new Cake ("4","D类蛋糕"));
        cakes.put("5",new Cake ("5","E类蛋糕"));
    }
    //获取所有数据
    public static Collection<Cake> findAllCakes(){
        return cakes.values();
    }

    //按编号获取蛋糕
    public static Cake findCakeById(String id){
        return cakes.get(id);
    }
}

3. Create a cake list handler

Create the net.xyx.session.servlet package, and then create the CakeListServlet class in the package to display a list of all available cakes. By clicking the "Buy" link, you can add the specified cake to the shopping cart.

4. Create a shopping handler

Create the PurchaseServlet class in the net.xyx.session.servlet package

package net.xyx.session.servlet;

import net.xyx.session.bean.Cake;
import net.xyx.session.dao.CakeDao;

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

@WebServlet(name = "PurchaseServlet")
public class PurchaseServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

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

//获取用户购买蛋糕的id
        String id = request.getParameter("id");
        //判断用户是否选购
        if(id != null){
            //按照id获取蛋糕对象
            Cake cake = CakeDao.findCakeById(id);
            // 创建或者获得用户的Session对象
            HttpSession session = request.getSession();
            // 从Session对象中获得用户的购物车
            List<Cake> cart = (List) session.getAttribute("cart");
            if (cart == null) { // // 首次购买
                // 为用户创建一个购物车(List集合模拟购物车)
                cart = new ArrayList<Cake>();
                // 将购物城存入Session对象
                session.setAttribute("cart", cart);
            }
            // 将商品放入购物车
            cart.add(cake);
            // 创建Cookie存放Session的标识号
            Cookie cookie = new Cookie("JSESSIONID", session.getId());
            cookie.setMaxAge(60 * 30);
            cookie.setPath("/Servlet");
            response.addCookie(cookie);
            // 重定向到购物车页面（CartServlet）
            response.sendRedirect("cart");

        } else {
            // 重定向到蛋糕列表显示页面（CakeListServlet）
            response.sendRedirect("cake_list");
        }
    }
}

5. Create a shopping cart handler

Create the CartServlet class in the net.xyx.session.servlet package

package net.xyx.session.servlet;

import net.xyx.session.bean.Cake;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

@WebServlet(name = "CartServlet")
public class CartServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 设置响应体内容类型
        response.setContentType("text/html; charset=utf-8");
        // 获取字符输出流
        PrintWriter out = response.getWriter();
        // 变量cart引用用户的购物车
        List<Cake> cart = null;
        // 变量hasPurchased标记用户是否买过商品
        boolean hasPurchased = true;
        // 获得用户的session
        HttpSession session = request.getSession(false);
        // 判断会话是否为空
        if (session == null) { // 尚未购买过商品
            hasPurchased = false;
        } else {
            // 获得用户购物车
            cart = (List) session.getAttribute("cart");
            // 判断购物车是否为空
            if (cart == null) { // 尚未购买过商品
                hasPurchased = false;
            }
        }

        out.print("<body style='text-align: center'>");
        // 判断用户是否购买过商品
        if (!hasPurchased) {
            out.print("遗憾，您尚未购买任何商品~<br>");
        } else {
            // 显示用户购买蛋糕的信息
            out.print("<h3>您购买的蛋糕</h3>");
            for (Cake cake : cart) {
                out.print(cake.getId() + " " + cake.getName() + "<br>");
            }
        }

    }

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

    }
}

6. You can then run the program to see the effect