【Cookie：默认存储在浏览器的内存中】显示上一次访问时间、商品浏览记录

Cookie的介绍：

Cookie是客户端技术，程序把每个用户的数据以cookie的形式写给用户各自的浏览器。当用户使用浏览器再去访问服务器中的web资源时，就会带着各自的数据去。

如果创建了一个cookie，并将他发送到浏览器，默认情况下它是一个会话级别的cookie（即存储在浏览器的内存中），用户退出浏览器之后即被删除。


1、Cookie显示上一次访问时间

cookie.setPath("/HelloJavaWeb/servlet/ServletDemo");  可以设置访问路径，不设置默认是/HelloJavaWeb/servlet/

package com.xiaozhi.controller;

import java.io.IOException;
import java.io.OutputStream;
import java.io.Writer;
import java.util.Date;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletDemo extends HttpServlet
{
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
response.setContentType("text/html;charset=utf-8");
Writer out=response.getWriter();

Cookie cookies[] = request.getCookies();
for (int i = 0; cookies != null && i < cookies.length; i++)
{
if (cookies[i].getName().equals("lastAccessTime"))
{
long cookieValue = Long.parseLong(cookies[i].getValue());
Date date = new Date(cookieValue);
out.write("上次访问时间:");
out.write(date.toLocaleString());
}
}

Cookie cookie = new Cookie("lastAccessTime", System.currentTimeMillis()+ "");
cookie.setMaxAge(3600);//设置cookie的有效时间长
cookie.setPath("/HelloJavaWeb/servlet/ServletDemo");
System.out.println(cookie.getPath());
response.addCookie(cookie);
}

protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
}
}

保存的位置：





2、删除Cookie的方法、路径必须一致

package com.xiaozhi.controller;

import java.io.IOException;
import java.io.OutputStream;
import java.util.Date;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletDemo2 extends HttpServlet
{
@Override
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException
{
Cookie cookie = new Cookie("lastAccessTime", System.currentTimeMillis()+ "");
cookie.setMaxAge(0);//覆盖并删除
cookie.setPath("/HelloJavaWeb");
response.addCookie(cookie);
}

protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException
{
}
}

到cookie文件夹下查看会发现已经删除

3、显示商品的浏览记录

记住一条开发原则：有检索数据的需求使用双列集合，没有检索数据的需求使用单列集合。

LinkedHashMap：保持原有的顺序

显示商品和浏览记录的Servlet

package com.xiaozhi.controller;

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;

public class CookieDemo extends HttpServlet
{

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
//1.输出所有商品
out.write("本站有如下商品:<br/>");
Map<String, Book> map = Db.getAll();
for (Map.Entry<String, Book> entry : map.entrySet())
{
Book book = entry.getValue();
out.print("<a href='" + request.getContextPath()+ "/servlet/CookieDemo2?id=" + book.getId() + "'>"+ book.getName() + "</a><br/>");

}

//4.显示用户看过的商品，这里显示三条浏览记录
out.print("<br/>你曾经看过的商品<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("\\,");// 2,3,1
for (String id : ids)
{
Book book = (Book) Db.getAll().get(id);
out.print("<a href='" + request.getContextPath()+ "/servlet/CookieDemo2?id=" + book.getId() + "'>"+ book.getName() + "</a><br/>");
}
}
}
}
}

class Db1
{
private static Map<String, Book> map = new LinkedHashMap<String, Book>();
static
{
map.put("1", new Book("1", "JavaWeb开发", "老方", "一本好书"));
map.put("2", new Book("2", "jdbc开发", "老张", "一本好书"));
map.put("3", new Book("3", "spring开发", "老黎", "一本好书"));
map.put("4", new Book("4", "struts开发", "老张", "一本好书"));
map.put("5", new Book("5", "android开发", "老毕", "一本好书"));
}

public static Map getAll()
{
return map;
}

}

class Book1
{
private String id;
private String name;
private String author;
private String description;

public Book1()
{
super();
}

public Book1(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;
}
}

查看商品详细信息的Servlet

package com.xiaozhi.controller;

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;

public class CookieDemo2 extends HttpServlet
{

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
//2.根据用户带过来的id，显示相应的详细信息
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();

String id = request.getParameter("id");
Book book = (Book) D
4000
b.getAll().get(id);
out.write(book.getId() + "<br/>");
out.write(book.getName() + "<br/>");
out.write(book.getAuthor() + "<br/>");
out.write(book.getDescription() + "<br/>");

//3.构建cookie，回写给浏览器；
String cookieValue = buildCookie(id, request);
Cookie cookie = new Cookie("bookHistory", cookieValue);
cookie.setMaxAge(1 * 30 * 24 * 3600);//1 个月
cookie.setPath(request.getContextPath()+"/servlet/");
response.addCookie(cookie);
}

private String buildCookie(String id, HttpServletRequest request)
{
// bookHistory =null  1  1
// bookHistory=2,5,1  1  1,2,5
// bookHistory=2,5,4  1  1,2,5
// bookHistroy=2,5    1  1,2,5
String bookHistroy = null;
Cookie cookies[] = request.getCookies();
for (int i = 0; cookies != null && i < cookies.length; i++)
{
if (cookies[i].getName().equals("bookHistory"))
{
bookHistroy = cookies[i].getValue();
}
}
if (bookHistroy == null)
return id;

LinkedList<String> linkedlist =new LinkedList<String>(Arrays.asList(bookHistroy.split("\\,")));
if (linkedlist.contains(id))
{
linkedlist.remove(id);
linkedlist.addFirst(id);
} else
{
if (linkedlist.size() >= 3)
{
linkedlist.removeLast();
linkedlist.addFirst(id);
} else
linkedlist.addFirst(id);
}
StringBuffer sb = new StringBuffer();
for (String bid : linkedlist)
{
sb.append(bid + ",");
}
return sb.deleteCharAt(sb.length() - 1).toString();
}

}