在购物网站中，最常见的一个功能就是当年浏览完几个商品之后，再次访问这个网站，网站会提醒你，你上次看了什么什么商品，或者当你选择好几个商品放入购物车时候最终的结账，都有这个东西，大概是使用Cookie实现的，最终还是Servlet的载入，下面就来实现这个案例

1.首先是首页执行显示的Servlet,他的功能是输出网站的所有商品和显示最近浏览过什么商品

package com.bird.cookie;import java.io.IOException;import java.io.PrintWriter;import java.util.LinkedHashMap;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * @category 网站的首页，用来显示所有的信息 * @author Bird * */public class CookieDemo2 extends HttpServlet { private static final long serialVersionUID = 1L; public void doGet(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  //解决乱码问题  response.setCharacterEncoding("UTF-8");//控制服务器编码方式  response.setContentType("text/html;charset=UTF-8");  PrintWriter out = response.getWriter();        //1.输出网站的所有商品  out.write("本网站有如下商品<br/>");  Map<String,Book> map = DB.getAll();  for(Map.Entry<String, Book> entry : map.entrySet()){   Book book = entry.getValue();   out.print("<a href='/WebDemo/servlet/CookieDemo3?id="+book.getId()+"' target='_blank'>"+book.getName()+"</a><br/>");  }    //2.显示用户看过的商品  out.write("<br/>您曾经看过如下商品<br/>");  Cookie cookies[] = request.getCookies();  for(int i = 0; cookies!=null && i < cookies.length; i++){   if(cookies[i].getName().equals("bookHistory")){    String []ids = cookies[i].getValue().split("\\,");    for(String s : ids){     Book book = DB.getAll().get(s);     out.write(book.getName()+"<br/>");    }   }  } }    public void doPost(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException { }}class DB{ //必须使用链表Map进行有序存储 private static Map<String,Book> map = new LinkedHashMap<String,Book>(); static{  map.put("1", new Book("1","javaweb开发详解","老张","一本好书!!!"));  map.put("2", new Book("2","jdbc开发详解","老张","一本好书!!!"));  map.put("3", new Book("3","sping开发详解","老黎","一本好书!!!"));  map.put("4", new Book("4","struts开发详解","老宇","一本好书!!!"));  map.put("5", new Book("5","heibrate开发详解","老毕","一本好书!!!")); }  public static Map<String,Book> getAll(){  return map; }}class Book{ private String id; private String name; private String author; private String description;  public Book(){}  public Book(String id, String name, String author, String description) {  this.id = id;  this.name = name;  this.author = author;  this.description = description; }  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 String getDescription() {  return description; } public void setDescription(String description) {  this.description = description; }  }

package com.bird.cookie;import java.io.IOException;import java.io.PrintWriter;import java.util.Arrays;import java.util.LinkedList;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * @category 显示商品的详细信息 * @author Bird * */public class CookieDemo3 extends HttpServlet { private static final long serialVersionUID = 1L; public void doGet(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  response.setCharacterEncoding("UTF-8");  response.setContentType("text/html;charset=UTF-8");  PrintWriter out = response.getWriter();    //1.根据用户提交的id显示对应的商品的详细的信息    String id = request.getParameter("id");  Book book = DB.getAll().get(id);  out.write("id为"+book.getId()+"<br/>");  out.write("书名为"+book.getName()+"<br/>");  out.write("作者为"+book.getAuthor()+"<br/>");  out.write("描述为"+book.getDescription()+"<br/>");    //2.构建Cookie,回写给浏览器  String cookieValue = buildCookie(id,request);  Cookie cookie = new Cookie("bookHistory",cookieValue);  cookie.setMaxAge(30*24*60*60);  cookie.setPath("/WebDemo");  response.addCookie(cookie); } private String buildCookie(String id, HttpServletRequest request) {  String bookHisttory = null;  Cookie [] cookies = request.getCookies();  for(int i = 0; cookies!=null && i < cookies.length; i++){   bookHisttory = cookies[i].getValue();  }    if(bookHisttory==null)   return id;    LinkedList<String> list = new LinkedList<String>(Arrays.asList(bookHisttory.split("\\,")));  if(list.contains(id)){   list.remove(id);  }else{   if(list.size()>=3){    list.removeLast();   }  }  list.addFirst(id);    StringBuffer sb = new StringBuffer();  for(String bid: list){   sb.append(bid + ",");  }  return sb.deleteCharAt(sb.length()-1).toString();//删除最后多余 的一个逗号  } public void doPost(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException { }}