Session案例之实现购物网址购物车

实现购物网址购物车
         要求：点击商品存入购物车购买，无论刷新还是关闭浏览器，都可以继续在购物车中继续购物，不会 损失掉之前所买的商品，并且用户禁用cookie也能实现。
首页，显示网站所有商品
public class IndexServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
//为了防止用户的第一次访问没有Session的情况，就创建一个Session
request.getSession();
//1.显示网站所有商品
out.print("本网站有如下书籍：<br/>");
Map<String,Book> map = DB.getMap();
for(Map.Entry<String, Book> entry : map.entrySet()){
Book book = entry.getValue();
//点击超链接购买就去找BuyServlet
String url = "/day07/servlet/BuyServlet?id="+book.getId();
//对于每一个购买都得到重写后的url，防止用户禁用cookie后无法实现多浏览器共享
url = response.encodeURL(url);
out.print(book.getName() + "<a href='"+url+"'>购买</a><br/>");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}

//模拟数据库
class DB{
private static Map<String,Book> map = new HashMap();
static{
map.put("1", new Book("1","javaweb开发","老张"));
map.put("2", new Book("2","jdbc开发","老黎"));
map.put("3", new Book("3","struts2开发","老张"));
map.put("4", new Book("4","spring开发","老黎"));
map.put("5", new Book("5","hibernate开发","老张"));
}
public static Map getMap(){
return map;
}
}
class Book implements Serializable{
private String id;
private String name;
private String author;
public Book() {
super();
// TODO Auto-generated constructor stub
}
public Book(String id, String name, String author) {
super();
this.id = id;
this.name = name;
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 String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
}

购买
public class BuyServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String id = request.getParameter("id");
Book book = (Book) DB.getMap().get(id);
//2.把用户买的书加在session中用于管理所有书的集合中了（注意不要直接往session中加，由于买的什么东西都加到session中，到最后结账就不知道什么类型了，为了方便就创建集合存入相同商品）
HttpSession session = request.getSession();
//为了实现多浏览器共享，帮助服务器回写Cookie，覆盖服务器自己发的Cookie
Cookie cookie = new Cookie("JSESSIONID",session.getId());
//设置Cookie的有效期为30分钟，不能设置时间过长，要不内存溢出
cookie.setMaxAge(30*60);
//设置有效路径
cookie.setPath("/day07");
//将Cookie发给浏览器
response.addCookie(cookie);
List list = (List) session.getAttribute("list");
//如果为空证明第一次购买
if(list==null){
list = new ArrayList();
session.setAttribute("list", list);
}
list.add(book);
//3.跳转到购物车显示列表（如果用forward，用户一刷新就又购买了一件）
//response对象的encodeRedirectURL方法实现了 url重写，防止用户禁用cookie后无法实现 多浏览器共享
String url = response.encodeRedirectURL("/day07/servlet/ListCartServlet");
response.sendRedirect(url);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}

显示用户买的所有书（购物车列表显示页面）
public class ListCartServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
out.print("您购买了如下商品:<br/>");
//集合中存储的是用户所买的书
List<Book> list = (List) request.getSession().getAttribute("list");
for(Book book : list){
out.print(book.getName() + "<br/>");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
注：此程序如果用户禁用了cookie就只能够通过超链接将session id传过去，这个过程称为URL重写。