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）

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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 + "]";    }}

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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);    }}

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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);    }}

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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);    }}

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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);    }}