Cookie和Session

第一章 会话技术简介

1.1 概述

• 会话：一次会话中包含多次请求和响应。

 

• 一次会话：浏览器第一次给服务器资源发送请求，会话建立，直到有一方断开为止。

1.2 功能

• 共享数据。

1.3 方式

• 客户端会话技术：Cookie。
• 服务器端会话技术：Session。

 

第二章 Cookie

2.1 概念

• 客户端会话技术，将数据保存在客户端。

2.2 快速入门

• 步骤：
• ① 创建Cookie对象，绑定数据。

public Cookie(String name, String value) 

• ②发送Cookie对象。

response.addCookie(cookie);

• ③获取Cookie对象。

Cookie[] cookies = request.getCookies();

 

• 示例：
• CookieDemoServlet.java

package com.sunxiaping.servlet;

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;

@WebServlet(urlPatterns = "/cookieDemoServlet")
public class CookieDemoServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1. 创建Cookie
        Cookie cookie = new Cookie("msg", "hello");
        //2. 发送Cookie对象
        response.addCookie(cookie);

        //重定向到CookieDemo2Servlet
        response.sendRedirect(request.getContextPath() + "/cookieDemo2Servlet");
    }

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

• CookieDemo2Servlet.java

package com.sunxiaping.servlet;

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;

@WebServlet(urlPatterns = "/cookieDemo2Servlet")
public class CookieDemo2Servlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取Cookie对象
        Cookie[] cookies = request.getCookies();
        if (null != cookies && cookies.length > 0) {
            for (Cookie cookie : cookies) {
                System.out.println("name:" + cookie.getName());
                System.out.println("value:" + cookie.getValue());
            }
        }

    }

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

2.2 实现原理

 

 

• 基于响应头set-cookie和请求头cookie实现的。

2.3 Cookie的细节

2.3.1 一次发送多个Cookie

• 示例：

package com.sunxiaping.servlet;

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;

@WebServlet(urlPatterns = "/cookieDemoServlet")
public class CookieDemoServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1. 创建Cookie
        Cookie cookie = new Cookie("msg", "hello");
        Cookie cookie1 = new Cookie("name","zhangsan");
        //2. 发送Cookie对象
        response.addCookie(cookie);
        response.addCookie(cookie1);

        
    }

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

2.3.2 Cookie在浏览器中的保存时间

• 默认情况下，当浏览器关闭后，Cookie中的数据自动销毁。

 

• 设置Cookie的保存路径以及时间：

public void setPath(String uri) {}

/**
* 正数，将Cookie数据写到硬盘中。持久化存储，表示Cookie的存活时间。
* 负数，默认值
* 0：删除Cookie信息
*/
public void setMaxAge() { }

 

• 示例：

package com.sunxiaping.servlet;

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;

@WebServlet(urlPatterns = "/cookieDemoServlet")
public class CookieDemoServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1. 创建Cookie
        Cookie cookie = new Cookie("msg", "hello");

        //设置Cookie的生命周期
        cookie.setPath(request.getContextPath());
        cookie.setMaxAge(60 * 5);

        //2. 发送Cookie对象
        response.addCookie(cookie);


    }

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

2.3.3 Cookie中存储中文

• Tomcat8之后Cookie支持存储中文。
• Tomcat7之前需要用URL编码将要存储到Cookie中的中文转码。

2.4 Cookie的特点和作用

• Cookie存储数据在客户端浏览器。
• 浏览器对于单个Cookie的大小有限制（4KB）以及对于同一个域名下的总Cookie数量有限制（20个）。

 

• 作用：
• ①Cookie一般用于存储少量的不太敏感的数据。
• ②在不登录的情况下，完成服务器对客户身份的识别。

 

第三章 Session

3.1 概念

• 服务器端会话技术，在一次会话的多次请求间共享数据，将数据保存在服务器端的对象中。HttpSession。

3.2 快速入门

• 获取HttpSession对象：

HttpSession session = request.getSession();

• 设置属性名和属性值：

public void setAttribute(String name, Object value);

• 根据属性名获取对应的属性值：

public Object getAttribute(String name);

• 移除属性：

public void removeAttribute(String name);

 

• 示例：

package com.sunxiaping.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(name = "SessionDemoServlet", urlPatterns = "/sessionDemoServlet")
public class SessionDemoServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();

        session.setAttribute("msg","hello");

        response.sendRedirect(request.getContextPath()+"/sessionDemo2Servlet");
    }

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

package com.sunxiaping.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(name = "SessionDemo2Servlet", urlPatterns = "/sessionDemo2Servlet")
public class SessionDemo2Servlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();

        Object msg = session.getAttribute("msg");

        System.out.println(msg);

    }

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

3.3 Session的特点

• Session用于存储一次会话的多次请求的数据，存储在服务器端。
• Session可以存储任意类型、任意大小的数据。