2019-04-28 JavaWeb之Cookie

作者: 果冻_4c9b | 来源:发表于2019-04-28 19:01 被阅读0次

2019-04-28 JavaWeb之Cookie
JavaWeb之Cookie
JavaWeb——Cookie
JavaWeb之Cookie和Session
JavaWeb之Cookie和Session
JavaWeb（九）Cookie
JavaWeb - Cookie/Session
JavaWeb基础之Cookie与Session
JavaWeb开发之状态管理Cookie
2019-04-28 JavaWeb之Session

在程序中，会话跟踪是很重要的事情。理论上，一个用户的所有请求操作都应该属于同一个会话，而另一个用户的所有请求操作则应该属于另一个会话，二者不能混淆。例如，用户A在超市购买的任何商品都应该放在A的购物车内，不论是用户A什么时间购买的，这都是属于同一个会话的，不能放入用户B或用户C的购物车内，这不属于同一个会话。
而Web应用程序是使用HTTP协议传输数据的。HTTP协议是无状态的协议。一旦数据交换完毕，客户端与服务器端的连接就会关闭，再次交换数据需要建立新的连接。这就意味着服务器无法从连接上跟踪会话。即用户A购买了一件商品放入购物车内，当再次购买商品时服务器已经无法判断该购买行为是属于用户A的会话还是用户B的会话了。要跟踪该会话，必须引入一种机制。
Cookie就是这样的一种机制。它可以弥补HTTP协议无状态的不足。在Session出现之前，基本上所有的网站都采用Cookie来跟踪会话。

Cookie默认是会话级别的，关闭浏览器就在浏览器内存中消失

重要方法

创建Cookie
Cookie cookie1 = new Cookie("java2_username", username);
设置持久化Cookie，以秒为单位，持久化的Cookie会保存在本地磁盘
cookie1.setMaxAge(60*60);

颁发Cookie
response.addCookie(cookie1);

典型应用 -- 记录登录名和密码

reLogin.java

<%@ 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>ReLogin Page</h1>
    <form action="${ pageContext.request.contextPath }/login2" method="post">
        <p><input type="text" name="username" value="${ java2_username }"></p>
        <p><input type="password" name="password" value="${ java2_password }"></p>
        <button>提交</button>
    </form>
</body>
</html>

Login2Servlet.java

package com.servlet;
import java.io.IOException;
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;

/**
 * Servlet implementation class Login2Servlet
 */
@WebServlet("/login2")
public class Login2Servlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.getWriter().append("Served at: ").append(request.getContextPath());
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        Userinfo user = new Userinfo();
        user.setUsername(username);
        user.setPassword(password);
        request.getSession().setAttribute("loginUser", user);
        
        // new
        Cookie cookie1 = new Cookie("java2_username", username);
        Cookie cookie2 = new Cookie("java2_password", password);
        // 磁盘
        cookie1.setMaxAge(60*60);
        cookie2.setMaxAge(60*60);
        response.addCookie(cookie1);
        response.addCookie(cookie2);
        
        response.sendRedirect(request.getContextPath()+"/success.jsp");
    }
}

GoReloginServlet.java

package com.servlet;
import java.io.IOException;
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;
/**
 * Servlet implementation class GoReloginServlet
 */
@WebServlet("/relogin")
public class GoReloginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    /**
     * @see HttpServlet#HttpServlet()
     */
    public GoReloginServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = "";
        String pass = "";
        Cookie cookies[] = request.getCookies();
        for(Cookie cookie : cookies){
            if(cookie.getName().equals("java2_username")){
                name = cookie.getValue();
            }
            if(cookie.getName().equals("java2_password")){
                pass = cookie.getValue();
            }
        }
        request.setAttribute("java2_username", name);
        request.setAttribute("java2_password", pass);
        request.getRequestDispatcher("/reLogin.jsp").forward(request, response);
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }
}