网页浏览历史纪录（Cookie技术）

package com.heima.demo1;
import java.io.IOException;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.heima.beans.Book;
public class ShowBookList extends HttpServlet
{
	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy()
	{
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException
	{
		// 准备图书信息
		ServletContext context = this.getServletContext();
		Map<String, Book> map = (Map<String, Book>) context.getAttribute("map");
		request.setAttribute("map", map);
		// 取出历史纪录
		List<Book> history = new ArrayList<Book>();
		Cookie[] cookies = request.getCookies();
		// 判断cookies是否为空，很重要，否者会出现无法获取数据，
		// 和空指针异常的错误
		if (cookies != null)
		{
			//遍历cookie数组
			for (Cookie c : cookies)
			{
				//找到带有历史信息的cookie
				if ("ids".equals(c.getName()))
				{
					//获取其中的数据
					String ids = c.getValue();
					//把原有的数据，切割成数组，取出每个书的编号信息
					String[] split = ids.split("-");
					for (String s : split)
					{
						//通过编号信息，取出对应的书
						Book b = map.get(s);
						// 把所有的书添加到一个list集合中，方便数据的传递						
						history.add(b);
					}
					//把数据设置到request域中
					request.setAttribute("history", history);
				}
			}
		}
		// 把准备好的数据发送到页面进行显示
		request.getRequestDispatcher("/showBookList.jsp").forward(request,
				response);
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException
	{
		doGet(request, response);
	}
	public void init() throws ServletException
	{
		//进行图书页面的显示图书的数据准备
		Map<String, Book> map = new LinkedHashMap<String, Book>();
		for (int i = 0; i < 10; i++)
		{
			Book b = new Book();
			b.setId(i + "");
			b.setName("java" + i);
			b.setNum(i);
			b.setPrice((i + 20) + "");
			// System.out.println(i);
			map.put(b.getId(), b);
		}
		//把拥有图书数据的map集合放到ServletContext域中，给所有程序共享
		this.getServletContext().setAttribute("map", map);
	}
}

package com.heima.demo1;
import java.io.IOException;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.heima.beans.Book;
public class ShowBookInfo extends HttpServlet
{
	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy()
	{
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException
	{
		// 获取ServletContext域中的map集合
		ServletContext context = this.getServletContext();
		Map<String, Book> map = (Map<String, Book>) context.getAttribute("map");
		// 获取图书编号
		String key = request.getParameter("id");
		Book b = map.get(key);
		// 创建浏览记录
		Cookie[] cookies = request.getCookies();
		// 用于判断是否是第一次访问
		boolean flag = true;
		// 判断cookies是否为空，很重要，否者会出现无法获取数据，
		// 和空指针异常的错误
		if (cookies != null)
		{
			//遍历数组
			for (Cookie cook : cookies)
			{
				//取出我们需要的历史纪录的数据
				if ("ids".equals(cook.getName()))
				{
					//如果有数据说明不是第一访问，把开关置为false
					flag = false;
					//获取cookie保存的数据
					String ids = cook.getValue();
					//按格式切割出我们原来的数据，这里是图书的编号
					String[] split = ids.split("-");
					//把数组转换为集合方便操作
					List<String> asList = Arrays.asList(split);
					LinkedList<String> list = new LinkedList(asList);
					//如果集合中包含当前访问的页面
					if (list.contains(key))
					{
						//把集合中的历史纪录删除
						list.remove(key);
					}
					//重新添加当前访问页面的纪录，添加在首歌
					list.addFirst(key);
					//把集合中的数据重新拼接成字符串数据，给Cookie保存
					StringBuffer sb = new StringBuffer();
					//只需要最大4次的访问记录
					for (int i = 0; i < list.size() && i < 4; i++)
					{
						sb.append(list.get(i));
						sb.append("-");
					}
					//把字符串末尾的“-”去除
					ids = sb.substring(0, sb.length() - 1);
					// System.out.println(ids);
					//重新创建一个名为ids的Cookies
					Cookie c = new Cookie("ids", ids);
					//向response域添加Cookie,覆盖原有Cookie
					response.addCookie(c);
				}
			}
		}
		//判断开关，如果为真则是第一次访问
		if (flag)
		{
			//新建名为ids的Cookie,保存当前访问的数据
			Cookie c = new Cookie("ids", key);
			//添加Cookie
			response.addCookie(c);
		}
		// 获取准备图书信息
		request.setAttribute("book", b);
		//把准备好的数据发送到显示页面
		request.getRequestDispatcher("/showBookInfo.jsp").forward(request,
				response);
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException
	{
		doGet(request, response);
	}
	/**
	 * Initialization of the servlet. <br>
	 * 
	 * @throws ServletException
	 *             if an error occurs
	 */
	public void init() throws ServletException
	{
	}
}

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	<h1>图书的详细信息</h1>
	<h3>图书名称：《${requestScope.book.name }》</h3>
	<h3>图书价格：${requestScope.book.price }</h3>
	<h3>图书描述：${requestScope.book.description }</h3>
	
	<h2><a href="/Test5/showBookList">返回图书列表</a></h2>
</body>
</html>