The previous article used a most commonly used user login registration program to explain the Servlet+JSP+JavaBean development model, so we also have a preliminary understanding of the Servlet+JSP+JavaBean (MVC) model. Now let's review this development model with a shopping cart program for online shopping.
Create a new day10 project in Eclipse, import the development package (jar package) required for the project, create the package required for the project, in java development , the architecture levels are reflected in the form of packages.
Development package (jar package) required for the project:
| Serial number | Development package name | Description |
|---|---|---|
| 1 | stl-1.2.jar | jstl tag library and EL expression dependency package |
Note: Different from the user login registration program in the previous article, this shopping cart program creates a class to represent the database, so there is no need to use other jar packages, just use Just go tostl-1.2.jar.
Packages required for the project:
The above are the packages created based on the actual situation of this project. You may also need to create other packages. This depends on the needs of the project.
Create a class representing the database:
Assume this is an online bookstore project, and the products purchased by users are books, so the products stored in the database are books. Create a DB class under the cn.itcast.DB package.
The specific code of the DB class is as follows:
public class DB { private static Map map = new LinkedHashMap(); static { map.put("1", new Book("1", "javaweb开发", "老张", 38, "一本好书")); map.put("2", new Book("2", "jdbc开发", "老黎", 18, "一本好书")); map.put("3", new Book("3", "ajax开发", "老佟", 328, "一本好书")); map.put("4", new Book("4", "jbpm开发", "老毕", 58, "一本好书")); map.put("5", new Book("5", "struts开发", "老方", 28, "一本好书")); map.put("6", new Book("6", "spring开发", "老方", 98, "一本好书")); } public static Map getAll() { return map; } }1234567891011121314151617
Note: Regarding how to create a class representing the database - DB.java, please refer to my Using Cookies for Session Management.
Create a jsp directory in the WEB-INF directory. The jsp directory stores some protected jsp pages of the system (users are not allowed to access directly through URL addresses). If users want to access these protected jsp pages, they can only Through the Servlet in the cn.itcast.web.UI package.
The created project architecture is shown in the figure below:
The code of the hierarchical architecture is also based on the [domain model layer (domain )] → [Data access layer (dao, dao.impl)] → [Business logic layer (service, service.impl)] → [Presentation layer (web.controller, web.UI, web.filter, web.listener)] It is written in the order of → [Tool class (util)] → [Test class (junit.test)].
Create a Book class under the cn.itcast.domain package.
The specific code of the Book class is as follows:
public class Book { private String id; private String name; private String author; private double price; private String description; public Book() { super(); // TODO Auto-generated constructor stub } public Book(String id, String name, String author, double price, String description) { super(); this.id = id; this.name = name; this.author = author; this.price = price; 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 double getPrice() { return price; } public void setPrice(double price) { this.price = price; } public String getDescription() { return description; } public void setDescription(String description) { this.description = description; } }1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253
Create a UserDao class under the cn.itcast.dao package.
The specific code of the UserDao class is as follows:
public class BookDao { public Map getAll() { return DB.getAll(); } public Book find(String id) { return DB.getAll().get(id); } }1234567891011
When we first developed a new project, we were not clear about it. The functions of all projects to be developed, so we can first develop the functions that are easiest to think of, and then disguise ourselves as a user. During the process of browsing the website pages, we see what functions the user needs, and then our programmers will develop what functions , and then work step by step to complete the functions of the entire project.
For example, when I first developed this shopping cart function module, the first thing I thought of was to display all the books to the user and query the book information based on the book ID. I didn't expect other functions, so I can wait until these functions are completed and see what functions are needed based on the front-end page.
Create a BusinessService class under the cn.itcast.service package.
First write the BusinessService class that implements the following two business services.
Show all books to users
Query book information based on book ID
Specific The code is as follows:
// 业务类，统一对web层提供所有服务public class BusinessService { private BookDao dao = new BookDao(); public Map getAllBook() { return dao.getAll(); } public Book findBook(String id) { return dao.find(id); } }12345678910111213
Written under the cn.itcast.web.controller package to process and display to users ListBookServlet for all books.
The specific code of the ListBookServlet class is as follows:
// 获取所有书public class ListBookServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { BusinessService service = new BusinessService(); Map map = service.getAllBook(); request.setAttribute("map", map); request.getRequestDispatcher("/WEB-INF/jsp/listbook.jsp").forward(request, response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }12345678910111213141516171819
Write the jsp page listbook.jsp in the /WEB-INF/jsp/ directory to display all books to the user.
Any jsp page located in the WEB-INF directory cannot be accessed directly through the URL address. During development, if there are some sensitive web resources in the project that you do not want to be directly accessed by the outside world, you can consider placing these sensitive web resources in the WEB-INF directory, so that outsiders can be prohibited from accessing them directly through URLs. The code of the
listbook.jsp page is as follows:
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%><%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>书籍列表页面 书籍列表
| 书名 | 作者 | 售价 | 描述 | 操作 |
| ${entry.value.name } | ${entry.value.author } | ${entry.value.price } | ${entry.value.description } | 购买 |
Websites generally have a homepage. In this project, in our homepage index.jsp, the user clicks theBrowse Bookshyperlink. All books on the website can be browsed. The code of the
index.jsp page is as follows:
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>网站首页 浏览书籍123456789101112
At this point, the development of the function of displaying all books to users is completed! Let’s test the developed function:
在现实中购买商品时，用户都是将商品放到购物车中，所以我们应该按照现实中的情况设计一个代表用户购物车的类——Cart.java。
现在再来思考一个问题：在设计代表用户购物车的Cart类时，应该使用private Book book字段(或属性)来代表用户所购买的商品吗？
答案显然不是。若是使用这样的字段，结果就是不可避免地在购物车中出现重复商品，即用户如果购买一本书多次，那么购物车中就出现一本书多次，显然在现实中这是不合理的。那么到底该怎么做呢？——为了避免在购物车里面出现重复商品，我们这时会设计一个专门的对象——CartItem（购物项，代表某个商品以及这个商品出现的次数）。
在cn.itcast.domain包下创建一个CartItem类，用于代表某个商品，以及商品出现的次数（购物项）。
CartItem类的具体代码如下：
// 用于代表某个商品，以及商品出现的次数（购物项）public class CartItem { private Book book; private int quantity; private double price; public Book getBook() { return book; } public void setBook(Book book) { this.book = book; } public int getQuantity() { return quantity; } public void setQuantity(int quantity) { this.quantity = quantity; this.price = this.book.getPrice() * this.quantity; } public double getPrice() { return price; } public void setPrice(double price) { this.price = price; } }12345678910111213141516171819202122232425262728
在cn.itcast.domain包中创建一个代表用户购物车的Cart类。
Cart类的具体代码如下：
// 代表用户的购物车public class Cart { /* * 为了避免在购物车里面出现重复商品， * 我们这时会设计一个专门的对象——CartItem(购物项，代表某个商品以及这个商品出现的次数) */ private Map map = new LinkedHashMap<>(); private double price; // 记住购物车中的所有商品多少钱 public void add(Book book) { // 看购物车中有没有，要添加的书对应的购物项 CartItem item = map.get(book.getId()); if(item==null) { item = new CartItem(); item.setBook(book); item.setQuantity(1); map.put(book.getId(), item); } else { item.setQuantity(item.getQuantity()+1); } } public Map getMap() { return map; } public void setMap(Map map) { this.map = map; } public double getPrice() { double totalprice = 0; for(Map.Entry entry : map.entrySet()) { CartItem item = entry.getValue(); totalprice += item.getPrice(); } this.price = totalprice; return price; } public void setPrice(double price) { this.price = price; } }12345678910111213141516171819202122232425262728293031323334353637383940414243
用户浏览网站首页时，会看到网站所有书籍，用户即可对自己感兴趣的书籍进行购买，点击购物超链接时，跳转到一个servlet对用户的请求进行处理。所以在cn.itcast.web.controller包中创建一个代表完成书籍购买的BuyServlet类。
BuyServlet类的具体代码如下：
// 完成书籍购买@WebServlet("/BuyServlet")public class BuyServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String id = request.getParameter("id"); BusinessService service = new BusinessService(); Book book = service.findBook(id); // 得到用户的购物车 Cart cart = (Cart) request.getSession().getAttribute("cart"); // 用户第一次购买，为用户创建购物车 if(cart==null) { cart = new Cart(); request.getSession().setAttribute("cart", cart); } // 把书加到用户的购物车中，完成购买 cart.add(book); /* * 浏览器重新访问地址：/WEB-INF/jsp/listcart.jsp * 但这个地址被保护起来，外面是无法直接访问的， * 要实现的话，会比较麻烦，需要先跳到servlet，然后再转到jsp。 */ // response.sendRedirect("/WEB-INF/jsp/listcart.jsp"); request.getRequestDispatcher("/WEB-INF/jsp/listcart.jsp").forward(request, response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }1234567891011121314151617181920212223242526272829303132333435363738
注意：显示购物车时，记住千万不要用请求转发，而应该使用重定向技术。若不是产生的后果可参考我的笔记Session——使用Session完成简单的购物功能。我上面的代码使用的是请求转发，这是不行的，读者要注意了啊！既然要使用重定向技术，下面这行代码可行吗？
response.sendRedirect("/WEB-INF/jsp/listcart.jsp");1
答案不言而喻，这是不行的。因为这是浏览器重新访问地址/WEB-INF/jsp/listcart.jsp，listcart.jsp页面是被保护起来了，外界是无法直接访问的。如果一定要实现的话，会比较麻烦，还需要先跳到一个servlet，然后再跳转到listcart.jsp。所以正规的做法是：BuyServlet类中使用重定向技术，即添加如下代码：
response.sendRedirect(request.getContextPath()+"/ListCartUIServlet");1
然后在cn.itcast.web.UI包下创建一个ListCartUIServlet类，专门用来接收请求之后转到jsp，给用户提供用户界面。
ListCartUIServlet类的具体代码如下：
public class ListCartUIServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.getRequestDispatcher("/WEB-INF/jsp/listcart.jsp").forward(request, response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }12345678910111213
这毕竟不是一个真实项目，所以不想把其搞得这么复杂哈！所以就干脆用了请求转发，但是读者一定要知道这还是不行的，要知道用重定向技术，怎么使用我也已经写的很明白了！
购物车显示页面listcart.jsp代码如下：
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
