public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  
  response.setCharacterEncoding("UTF-8");
  response.setContentType("text/html;charset=utf-8");
  
  PrintWriter writer = response.getWriter();
  writer.write("您上次访问的时间是：");
  //获取用户上一次的访问时间并显示
  Cookie[] cookies = request.getCookies();   //从请求中获取客户端发来的Cookie
  for(int i=0;cookies!=null && i<cookies.length;i++) {
   if(cookies[i].getName().equals("lastAccessTime")) { //获取最后访问时间的Cookie
    Long mTime = Long.parseLong(cookies[i].getValue());  
    String lastAccessTime = new Date(mTime).toLocaleString();
    writer.write(lastAccessTime);
   }
  }
  //将本次登录时间重新装载进Cookie中并返回给客户端
  Cookie timeCookie = new Cookie("lastAccessTime", System.currentTimeMillis()+"");
  timeCookie.setMaxAge(1*24*60*60); //将Cookie有效期置为一天
  response.addCookie(timeCookie);  //将Cookie传回客户端
 }

public class Product {
 
 private String id;
 private String name;
 private String author;
 
 public Product() {
  super();
  
 }
 public Product(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;
 }
}

public class ProductDatabase {
 
 private static Map<String,Product> map = new HashMap<String, Product>();
 
 static{
  map.put("1", new Product("1","《Java编程思想》","JB"));
  map.put("2", new Product("2","《Java核心技术》","fdaf"));
  map.put("3", new Product("3","《Java并发编程》","什么鬼"));
  map.put("4", new Product("4","《Head first 设计模式》","老王"));
  map.put("5", new Product("5","《HTML5权威手册》","hhaa"));
 }
 
 public static Map<String,Product> getMap() {
 
  return map;
 }
 
}

response.setCharacterEncoding("UTF-8");
  response.setContentType("text/html;charset=utf-8");
  
  PrintWriter writer = response.getWriter();
  //从数据库中取出要显示在购物网站首页的商品
  Map<String,Product> map = ProductDatabase.getMap();
  if(map == null) {
   writer.print("您访问的宝贝已下架");
   return ;
  }
  for(Map.Entry<String, Product> en : map.entrySet()) {
   writer.print("<a href='/CookieProductProject/servlet/DetailGoodServlet?id="+en.getKey()+"' target='_blank' >"
              +en.getValue().getName()+" <br/>");
  }
  
  
  //显示用户之前浏览过的商品,要从用户发送的请求中的Cookie里取得
  writer.print("<br/><br/>");
  writer.print("您最近浏览过的商品： <br/>");
  
  Cookie[] cookies = request.getCookies();
  for(int i=0;cookies!=null && i<cookies.length;i++ ) {
   if(cookies[i].getName().equals("productHistory")) {
    Cookie cookie = cookies[i];
    String productId = cookie.getValue();
    String[] splitId = productId.split("\\_");
    for(String sId:splitId) {
     Product book = ProductDatabase.getMap().get(sId);
     writer.print(book.getName()+"<br/>");
    }
   }
  }
}

response.setCharacterEncoding("UTF-8");
  response.setContentType("text/html;charset=UTF-8");
  PrintWriter writer = response.getWriter();

  //通过用户点击商品的超链接而跟随URL来的ID参数来获取商品的详细信息
  String productId = request.getParameter("id");
  Map<String, Product> map = ProductDatabase.getMap();
  Product book = map.get(productId);
  writer.print("商品名："+book.getName()+"<br />");
  writer.print("作者："+book.getAuthor());
  
  //同时通过Cookie将用户观看的商品以Cookie的形式回传给用户浏览器 
  Cookie[] allCookies = request.getCookies();
  
  Cookie cookie = creCookie(book.getId(),allCookies);
  cookie.setMaxAge(24*60*60);
  response.addCookie(cookie);

private Cookie creCookie(String id, Cookie[] cookies) {
  Cookie cookie = null;
  
  if(cookies == null) { //如果cookies为空，说明用户首次访问
   cookie = new Cookie("productHistory", id);
   System.out.println(cookie.getValue());
   return cookie;
  }
  for(int i=0; i<cookies.length; i++) {
   if(cookies[i].getName().equals("productHistory")){
    cookie = cookies[i];
   }
  }
  
  String historyStr = cookie.getValue(); //此时获取到的之前浏览过数据的历史记录，有多种情况
  String[] produIds = historyStr.split("\\_");
  
  //为了检测数组中是否有包含当前的id，建议使用集合，而且是使用链表结构的集合
  LinkedList<String> list = new LinkedList<String>(Arrays.asList(produIds));
  if(list.contains(id)) {
   list.remove(id);
  }
  else if(list.size()>=3){
    list.removeLast();
  }
  
  list.addFirst(id);
  
  StringBuilder sb = new StringBuilder();
  for(String sId :list) {
   sb.append(sId+"_");
  }
  sb.deleteCharAt(sb.length()-1); 
  cookie.setValue(sb.toString());
  System.out.println(cookie.getValue());
  return cookie;
}