Session 快速开始 通过session的attribute通信

【web.xml】

<session-config>
    <session-timeout>30</session-timeout>
    <cookie-config>
        <!--<name>JSESSIONID</name>-->
        <!--<domain>net.mypla</domain>-->
        <!--<path>/shop</path>-->
        <!--<comment><![CDATA[Keeps you logged in.See our privacy policy for more information]]></comment>-->
        <http-only>true</http-only><!--Flash RIA不让访问-->
        <!--<secure>false</secure>&lt;!&ndash;如果使用了HTTPS设为true&ndash;&gt;-->
        <!--<max-age>1800</max-age>-->
    </cookie-config>
    <tracking-mode>COOKIE</tracking-mode><!--顺序很重要 首选cookie-->
    <!--<tracking-mode>URL</tracking-mode>-->
    <!--<tracking-mode>SSL</tracking-mode>-->
</session-config>

【StoreServlet】

@WebServlet(name="storeServlet",urlPatterns = {"/shop"})
public class StoreServlet extends HttpServlet{
    private final Map<Integer,String> products = new Hashtable<>();

    public StoreServlet(){
        this.products.put(1,"Sandpaper");
        this.products.put(2,"Nails");
        this.products.put(3,"Glue");
        this.products.put(4,"Paint");
        this.products.put(5,"Tape");
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String action = req.getParameter("action");
        if (action==null){
            action = "browse";
        }
        switch (action){
            case "addToCart":
                this.addToCart(req,resp);
                break;
            case "viewCart":
                this.viewCart(req,resp);
                break;
            case "browse":
            default:
                this.browse(req,resp);
                break;
        }
    }

    private void browse(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setAttribute("products",this.products);
        req.getRequestDispatcher("/WEB-INF/jsp/view/browse.jsp").forward(req,resp);
    }

    private void viewCart(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setAttribute("products",this.products);
        req.getRequestDispatcher("/WEB-INF/jsp/view/viewCart.jsp").forward(req,resp);

    }

    private void addToCart(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        int productId;
        try{
            productId = Integer.parseInt(req.getParameter("productId"));
        }catch (Exception e){
            resp.sendRedirect("shop");
            return;
        }

        //cart的结构 <productId,qty>
        //准备把购物车商品保存在session当中
        HttpSession session = req.getSession();
        //如果先前已经有
        if(session.getAttribute("cart") == null) {
            session.setAttribute("cart", new Hashtable<Integer, Integer>());
        }

        @SuppressWarnings("unchecked")
        Map<Integer,Integer> cart = (Map<Integer, Integer>) session.getAttribute("cart");
        if (!cart.containsKey(productId)){
            cart.put(productId,0);
        }
        cart.put(productId,cart.get(productId)+1);

        resp.sendRedirect("shop?action=viewCart");
    }
}

【browse.jsp】

<h2>商品列表</h2>
<a href="<c:url value="/shop?action=viewCart"/>">View Cart</a><br /><br />
<%
    @SuppressWarnings("unchecked")
    Map<Integer,String> products = (Map<Integer, String>) request.getAttribute("products");
    for (int id:products.keySet()){
        %><a href="<c:url value="/shop"><c:param name="action" value="addToCart"/>
        <c:param name="productId" value="<%=Integer.toString(id)%>"/>
        </c:url>"><%=products.get(id)%><br /></a><%
    }
%>
【viewCart.jsp】

<h2>查看购物车</h2>
<a href="<c:url value="/shop"/>">商品列表</a><br/><br/>
<%
    @SuppressWarnings("unchecked")
    Map<Integer,String> products = (Map<Integer, String>) request.getAttribute("products");
    @SuppressWarnings("unchecked")
    Map<Integer,Integer> cart = (Map<Integer, Integer>) session.getAttribute("cart");

    if (cart == null || cart.size()==0){
        out.println("购物车是空空的");
    }else{
        for (int id:cart.keySet()){
            out.println(products.get(id)+"(数量: "+cart.get(id)+")<br/>");
        }
    }
%>