session转化为cookie？？？？？？？？？？

HttpSession session=request.getSession(true);
ArrayList previousItems=(ArrayList)session.getAttribute("previousItems");
if(previousItems == null){
previousItems=new ArrayList();
session.setAttribute("previousItems", previousItems);
}
String newItem=request.getParameter("newItem");
String title="Item Purchased";
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
out.println("

"); //wo xie de
try {
synchronized(previousItems){
if(newItem !=null){
previousItems.add(newItem);
}
if(previousItems.isEmpty()){
out.println("No Items");
}else{
out.println("Items:");
out.println("

");
for(int i=0; i out.println("
• "+(String)previousItems.get(i)+"
");
}
out.println("

");
}
}
session.invalidate();
out.println("Back");

    } finally {            
        out.close();
    }


        想请问一下这个怎么用cookie实现