用session实现简单的购物车功能

使用servlet中的session实现简单的购物车功能（显示商品，点击添加到购物车，查看购物车）

---

以书为例，首先创建Book类

public class Book {
    private String id;
    private String name;
    private double price;
    private String author;

    public Book(){}
    public Book(String id, String name, double price, String author) {
        super();
        this.id = id;
        this.name = name;
        this.price = price;
        this.author = author;
    }
    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 double getPrice() {
        return price;
    }
    public void setPrice(double price) {
        this.price = price;
    }
    public String getAuthor() {
        return author;
    }
    public void setAuthor(String author) {
        this.author = author;
    }
    //重写toString()方法
    @Override
    public String toString() {
        return "Book [id=" + id + ", name=" + name + ", price=" + price
                + ", author=" + author + "]";
    }
}

---

简单的实现数据库端，直接写入几条数据

public class DBUtil {
    private static Map<String,Book> books = new HashMap<String,Book>();
    static{
        books.put("1", new Book("1","红楼梦",120,"曹雪芹"));
        books.put("2", new Book("2","西游记",120,"吴承恩"));
        books.put("3", new Book("3","水浒",120,"施耐庵"));
        books.put("4", new Book("4","三国演义",120,"罗贯中"));
    }
    /**
     * 得到所有书的方法
     */
    public static Map<String,Book> getAllBooks()
    {
        return books;
    }
    /**
     * 根据书的id得到书对象
     */
    public static Book findBookById(String id)
    {
        return books.get(id);
    }

}

---

下面实现在页面中显示所有的书

public class ShowAllBooks extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //显示所有书籍的servlet
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        out.println("<h2>本网站所有书籍如下:</h2>");
        //得到所有书籍
        Map<String,Book> books = DBUtil.getAllBooks();

        for(Map.Entry<String, Book> en:books.entrySet())
        {
            String key = en.getKey();
            Book book = en.getValue();
            //点击书籍名称跳转到AddToCar中，添加到购物车
            String url = request.getContextPath()+"/servlet/addtocar?id="+key;
            out.println("<a href='"+url+"'>"+book.getName()+"</a><br/>");
        }
        //点击查看购物车，跳转到ShowCar中
        String path = request.getContextPath()+"/servlet/showcar";
        out.println("<a href='"+path+"'>查看购物车</a>");
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        doGet(request,response);
    }
}

---

添加到购物车中的功能实现

public class AddToCar extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        //把书添加到购物车的Servlet
        String bookid = request.getParameter("id");//得到书的id

        //根据书的id得到书对象
        Book book = DBUtil.findBookById(bookid);

        //把书放到购物车  ---用集合当购物车，车放到 session中
        HttpSession session = request.getSession();

        //得到购物车
        List<Book> list = (List<Book>) session.getAttribute("car");

        if(list==null){
            list = new ArrayList<Book>();
        }
        list.add(book);//把书放到购物车

        //把购物车放到 Session
        session.setAttribute("car", list);
        PrintWriter out = response.getWriter();
        out.println("添加成功!");
        //转到首页
        response.setHeader("refresh", "2;url='"+request.getContextPath()+"/servlet/showallbooks'");
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

---

显示购物车中的书籍：

public class ShowCar extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //显示购物车中所有书的Servlet
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        HttpSession session = request.getSession();
        //得到购物车
        List<Book> list =(List<Book>) session.getAttribute("car");
        if(list==null){
            out.println("你还什么都没买呢!!!");
            response.setHeader("refresh", "2;url='"+request.getContextPath()+"/servlet/showallbooks'");
        }
        else{
            for(Book book:list)
            {                       out.println(book.getName()+","+book.getPrice()+","+book.getAuthor()+"<br/>");
            }
        }
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request,response);
    }
}