cookie案例之显示用户上次浏览过的商品

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//网站首页
public class CookieDemo2 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//有中文输入，防止乱码response.setContentType("text/html;charset=UTF-8");response.setCharacterEncoding("UTF-8");PrintWriter  out = response.getWriter();//1.显示网站所有商品//print与write的区别在于有换行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();out.print("<a href='/day07/servlet/CookieDemo3?id="+book.getId()+"' target='_blank'>"+book.getName()+"</a><br/>");}out.print("您曾经看过如下商品：<br/>");//2.显示用户曾经浏览过的商品    //   bookHistoryCookie cookie = null;Cookie cookies[] = request.getCookies();for(int i=0;cookies!=null && i<cookies.length;i++){if(cookies[i].getName().equals("bookHistory")){cookie = cookies[i];}}if(cookie!=null){//找到了bookHistory这个cookie//值为这样的：4_6_1String bookHistory = cookie.getValue(); //以_分割字符串，需要转义String ids[] = bookHistory.split("\\_");for(String id: ids){Book book = (Book) DB.getMap().get(id);out.print(book.getName() + "<br/>");}}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}
}//此类用于模拟数据库
class DB{//用map集合的原因为要用到检索数据的需求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"));}//提供方法返回map集合public static Map getMap(){return map;}
}
class Book{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;}
}//显示商品详细信息
public class CookieDemo3 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();//1.根据用户带过来的id值，显示相应商品的信息out.print("您想看的书的详细信息为：<br/>");String id = request.getParameter("id");Book book = (Book) DB.getMap().get(id);out.print(book.getId() + "<br/>");out.print(book.getName() + "<br/>");out.print(book.getAuthor() + "<br/>");//2.以cookie的形式回写该商品的id号给浏览器String bookHistory = makeCookie(book.getId(),request);Cookie cookie = new Cookie("bookHistory",bookHistory);cookie.setMaxAge(10000);response.addCookie(cookie);}//根据用户原来看过的书，以及现在看的书的id，构建新的cookie值（要求浏览历史只能保存3本书）private String makeCookie(String id, HttpServletRequest request) {//有以下四种情况//首次看id为3的书//bookHistory=null    3     bookHistory=3//浏览历史有三个了，但不包含id等于3的书，要删除最后一个再把3加在开头//bookHistory=2_1_5   3     bookHistory=3_2_1//浏览历史不超过3个，直接把3加在开头//bookHistory=2       3     bookHistory=3_2//浏览历史包含id为3的书，将其删除，再添加到开头//bookHistory=2_3     3     bookHistory=3_2//1.得到用户曾经看过的书String bookHistory = null;Cookie cookies[] = request.getCookies();for(int i=0;cookies!=null && i<cookies.length;i++){if(cookies[i].getName().equals("bookHistory")){bookHistory = cookies[i].getValue();}}//等于空证明用户第一次访问if(bookHistory==null){bookHistory = id;return bookHistory;}//bookHistory=1_2_5    代表用户曾经看一些书，接着程序要得到用户曾经看过什么书//先切割成含有id的数组String ids[] = bookHistory.split("_");//为了检测数组中是否包含当前id，我们应该把数据转成集合，并且还要转成链表结构的集合，为了使用addFirst方法与removelast方法LinkedList<String> idList = new LinkedList(Arrays.asList(ids));//如果包含，就移除if(idList.contains(id)){idList.remove(id);}else{//如果不包含且长度够了，就删除最后一个if(idList.size()>=3){idList.removeLast();}}//总之都要在开头添加此ididList.addFirst(id);//再将id与_连接组合形成新的cookies的值，但末尾存在_StringBuffer sb = new StringBuffer();for(String lid: idList){   //1_2_3_sb.append(lid + "_");}//把末尾的_截取return sb.deleteCharAt(sb.length()-1).toString();}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}
}

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