cookie和session

会话

会话:用户打开浏览器，浏览页面，直到关闭浏览器的过程称为一次会话。
会话跟踪技术包括： Cookie（客户端技术）
                Session（服务器端技术）

cookie

  服务器负责：
　　　　　　　负责写cookie

　　　　　　　负责解析浏览器传过来的cookie

　浏览器负责：

　　　　　　　负责保存cookie

　　　　　　　负责将cookie发送给服务器

　　　　　　　浏览器一般只允许存放300个Cookie，每个站点最多存放20个Cookie（新版本的浏览器有所提升），每个Cookie的大小限制为4KB。

　Cookie常用方法:

　　　　　　　Cookie c = new Cookie(“”,“”) 构造方法

　　　　　　　c.getName()  获取cookie名

　　　　　　　c.getValue()  获取value值

　　　　　　　c.setMaxAge(int 秒)   设置存活时间

　　　　　　　setPath()　　　　设置有效路径

　　　　　　　Cookies[] cookie = request.getCookies(); 获得浏览器带来的cookie

　　　　　　　response.addCookie(cookie);将cookie带回浏览器
　　　　　　　
　　　　　　　乱码问题解决

　　　　　　　　　　编码：URLEncoder.encode(loginName,"utf-8");

　　　　　　　　　　解码：URLDecoder.decode("","UTF-8);

案例1  是否是第一次访问:

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
@WebServlet(name = "w1",urlPatterns = "/w1")
public class work1 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        Cookie[] cs = request.getCookies();
        PrintWriter out = response.getWriter();

        boolean flag = false;

        if(cs!=null){
            for(Cookie c:cs){
                if("visited".equals(c.getName())){
                    flag = true;
                    break;
                }
            }
        }
        if (flag){
            out.println("欢迎回来");
        }else{
            out.println("第一次访问");
            Cookie cookie = new Cookie("visited", "visit");
            cookie.setMaxAge(24*60*60);
            response.addCookie(cookie);
        }
    }
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

案例2:   记录客户端上次访问时间:

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.time.LocalDateTime;
@WebServlet(name = "w2",urlPatterns = "/w2")
public class Work2 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        Cookie[] cs = request.getCookies();
        PrintWriter out = response.getWriter();
        boolean flag = false;
        Cookie cookie=null;
        if(cs!=null){
            for(Cookie c:cs){
                if("visited2".equals(c.getName())){
                    flag = true;
                    cookie=c;
                    break;
                }
            }
        }
        if (flag){
            out.print("欢迎回来");
            out.print("<h1>上次访问时间为："+cookie.getValue()+"</h1>");
        }else{
            out.println("第一次访问");
        }
        Cookie cookie1 = new Cookie("visited2", LocalDateTime.now().toString());
        cookie.setMaxAge(24*60*60);
        response.addCookie(cookie1);
    }
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

案例3:   记录客户访问次数:

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.time.LocalDateTime;
@WebServlet(name = "w3",urlPatterns = "/w3")
public class work3 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        Cookie[] cs = request.getCookies();
        PrintWriter out = response.getWriter();

        boolean flag = false;
        Cookie cookie=null;
        if(cs!=null){
            for(Cookie c:cs){
                if("visited3".equals(c.getName())){
                    flag = true;
                    cookie=c;
                    break;
                }
            }
        }
        int i = 0;
        if (flag){
            i = Integer.parseInt(cookie.getValue());
            out.print("欢迎回来");
            out.print("<h1>访问次数为："+(++i)+"</h1>");
        }else{
            out.println("第一次访问");
            Cookie cookie1 = new Cookie("visited3", 1+"");
            cookie1.setMaxAge(24*60*60);
            response.addCookie(cookie1);
        }
        cookie = new Cookie("visited3", i+"");
        response.addCookie(cookie);

    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

案例4:   记录客户端用户名:

@WebServlet(name = "username",urlPatterns = "/username")
public class login extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String loginName = request.getParameter("loginName");
        String password  = request.getParameter("pwd");
        String remember = request.getParameter("remember");
        int num = Integer.parseInt(remember);

        if("123".equals(loginName.trim()) && "123".equals(password.trim())){
            //登录成功,记录登录名
            if(num!=0){
                String name = URLEncoder.encode(loginName, "UTF-8");// 编码
                Cookie c = new Cookie("loginName",name);
                c.setMaxAge(num*24*60*60);
                response.addCookie(c);
            }
        }else{
            response.sendRedirect("loginUsername.jsp");
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,  response);
    }
}

案例5:  记录用户的浏览记录:(网站的真实案例)

@WebServlet(name = "username",urlPatterns = "/username")
public class login extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String loginName = request.getParameter("loginName");
        String password  = request.getParameter("pwd");
        String remember = request.getParameter("remember");
        int num = Integer.parseInt(remember);

        if("123".equals(loginName.trim()) && "123".equals(password.trim())){
            //登录成功,记录登录名
            if(num!=0){
                String name = URLEncoder.encode(loginName, "UTF-8");// 编码
                Cookie c = new Cookie("loginName",name);
                c.setMaxAge(num*24*60*60);
                response.addCookie(c);
            }
        }else{
            response.sendRedirect("loginUsername.jsp");
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,  response);
    }
}

<%@ page import="com.cc.utils.CookieUtils" %>
<%@ page import="java.util.Arrays" %><%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2019/8/30
  Time: 16:26
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title></title>
  </head>
  <body>
    <a href="ServletView?id=1"><img src="img/1.jpg" />手电筒</a>
    <a href="ServletView?id=2"><img src="img/2.jpg" />手机</a>
    <a href="ServletView?id=3"><img src="img/3.jpg" />电视</a>
    <a href="ServletView?id=4"><img src="img/4.jpg" />冰箱</a>
    <a href="ServletView?id=5"><img src="img/5.jpg" />手表</a>
    <a href="ServletView?id=6"><img src="img/6.jpg" />电脑</a>
    <hr />
    <%
      Cookie[] cs = request.getCookies();
      Cookie c = CookieUtils.findCookieByName("product", cs);
      if(c!=null){
        String value = c.getValue();
        String[] ss = value.split(",");
        for(String str:ss){
    %>
    <img src="img/<%=str%>.jpg" width="150" height="100" />
    <%
        }
      }
    %>
  </body>
</html>


<%@ 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></title>
</head>
<body>
   <%
       String id = (String)request.getAttribute("id");
   %>
   <img src="img/<%=id %>.jpg" width="300" height="400" />
   <a href="index.jsp">返回首页</a>
</body>
</html>

session

和cookie的区别
　　1 Cookie有大小和个数的限制的.  Session存在服务器端没有大小和个数的限制.
　　2 Cookie存到客户端上 信息不安全.  Session的数据相对来说安全.

　　　3.Session运行原理也是基于Cookie ：利用Cookie回写一个 JSESSIONID 

　session方法

　　　HttpSession session = request.getSession();  创建session

　　　HttpSession session = request.getSession(false);  若没有创建,返回null

　　　session.getId(); 获取session的ID;

　　　session.setAttribute("",Object);  　写入信息

   　session.getAttribute("");   获取信息

   　session.removeAttribute("");  移除信息

　session的销毁

　　　1.关闭服务器（非正常关闭服务器）

　　　2.session时间到期 session的默认存活时间是30分钟

　　　3.调用session 的  invalidate()方法

　典型应用

　　　Web工程HttpSession的最典型应用是，登录时，当登录成功后，把登录用户的对象保存在Session中，保证一次会话该用户的状态。退出登录时，把该用户从Session中清除。

　Session和Cookie的区别和联系

　　 　1.数据存储的位置不同 Cookie在客户端 Session在服务器端

      2.生命周期不同,Cookie（会话Cookie浏览器关闭   持久化Cookie setMaxAge(秒数)）Session(默认30分钟，可以修改)

      3.cookie只能存放字符串名值对，session可以是任意对象

      4.同一个浏览器接受cookie的个数是有上限

案例1  是否是第一次访问:

public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String str = "";
        HttpSession session = request.getSession(false);
        if(session==null){
            str = "第一次访问";
            session = request.getSession();
        }else{            
            str = "欢迎回来";
        }
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        out.println(str);    
    }

案例2  典型应用登录后保存用户信息:

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        UserService service = new  UserServiceImpl();
        response.setContentType("text/html;charset=utf-8");
        User user = service.login(username, password);
        ServletContext sc= this.getServletContext();
        if(user!=null){
            //传入session
            HttpSession session = request.getSession(false);
            session.setAttribute("user",user);
            response.sendRedirect("welcome.jsp");
        }else{
            response.sendRedirect("login.jsp");
        }
    }

<%@ page import="com.cc.bean.User" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<html>
<title>Insert title here</title>
<script>
    function changeImage(){
        document.getElementById('checkImage').src="CheckCodeServlet?aaa="+Math.random();
    }
</script>
</head>
<body>
<%
    User user = (User)session.getAttribute("user");
    String str = "";
    if (user!=null){
        str = user.getUsername();
        System.out.println(str);
    }
%>
<form action="Servlet" method="post">
    username:<input type="text" name="username" value="<%=str%>"/><br/>
    password:<input type="password" name="password" /><br/>
    验证码:<input type="text" size="10" /><img src="CheckCodeServlet" id="checkImage" /><a href="javascript:changeImage()">看不清，换一张</a><br/>
    <input type="submit" value=" login " />
</form>

</body>
</html>