//获得要查询的商品的pid
String pid = request.getParameter("pid");
//获得客户端携带cookie---获得名字是pids的cookie
String pids = pid;
Cookie[] cookies = request.getCookies();
if(cookies!=null){
for(Cookie cookie : cookies){
if("pids".equals(cookie.getName())){
pids = cookie.getValue();
//1-3-2 本次访问商品pid是8----->8-1-3-2
//1-3-2 本次访问商品pid是3----->3-1-2
//1-3-2 本次访问商品pid是2----->2-1-3
//将pids拆成一个数组
String[] split = pids.split("-");//{3,1,2}
List<String> asList = Arrays.asList(split);//[3,1,2]
LinkedList<String> list = new LinkedList<String>(asList);//[3,1,2]
//判断集合中是否存在当前pid
if(list.contains(pid)){
//包含当前查看商品的pid
list.remove(pid);
list.addFirst(pid);
}else{
//不包含当前查看商品的pid 直接将该pid放到头上
list.addFirst(pid);
}
//将[3,1,2]转成3-1-2字符串
StringBuffer sb = new StringBuffer();
for(int i=0;i<list.size()&&i<7;i++){
sb.append(list.get(i));
sb.append("-");//3-1-2-
}
//去掉3-1-2-后的-
pids = sb.substring(0, sb.length()-1);
}
}
}

Cookie cookie_pids = new Cookie("pids",pids);
response.addCookie(cookie_pids);