060_Cookie/Session

时间 2021-03-18

标签 html java web apache api 数组浏览器服务器 cookie session 栏目 HTML 繁體版

原文原文链接

会话

用户打开一个浏览器到关闭浏览器，这个过程能够称之为会话。html

有状态会话

客户端再次访问服务端时，服务端知道客户端曾经来过，称之为有状态会话。java

保存会话的两种技术

客户端技术（响应，请求）

session

服务端技术，利用这个技术，能够保存用户的会话信息，咱们能够把信息或数据放在session中

常见场景

网站登陆后，下次访问不须要登陆

服务端响应给客户端cookie
服务端从客户端请求中拿到cookie

Cookie[] cookies = req.getCookies();//获取cookie
cookie.getName();//获取cookie的key
cookie.getValue();//获取cookie的value
Cookie cookie = new Cookie("lastLoginTime",String.valueOf(System.currentTimeMillis()));//新建cookie
cookie.setMaxAge(24*60*60);//设置cookie有效期设置为1天
resp.addCookie(cookie);//响应给客户端一个cookie

cookie通常会保存在本地的用户目录下的appData目录下

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.qing</groupId>
  <artifactId>javaweb-cookie-session</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>

  <dependencies>
    <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>4.0.1</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api -->
    <dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>javax.servlet.jsp-api</artifactId>
      <version>2.3.3</version>
    </dependency>
  </dependencies>
</project>

package com.qing.servlet;

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

/**
 * 保存用户上一次访问的时间
 */
public class CookieDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //服务器告诉你，你来的时间，把这个时间封装为一个信件，下次来时，带上信件，服务器就知道你又来了
        //简单解决中文乱码问题
        req.setCharacterEncoding("UTF-8");
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=utf-8");

        PrintWriter out = resp.getWriter();

        //Cookie，服务端从客户端获取
        Cookie[] cookies = req.getCookies();//这里返回数组，说明cookie可能存在多个
        //判断cookie是否存在，第一次访问服务器时，不存在，cookie是由服务器给客户端的
        if (cookies == null || cookies.length < 1) {
            out.write("这是您第一次访问本站");
        } else {
            //若是存在，读取cookie，获取cookie中的值
            boolean flag = true;
            for (int i = 0; i < cookies.length; i++) {
                Cookie cookie = cookies[i];
                if ("lastLoginTime".equals(cookie.getName())) {
                    flag = false;
                    out.write("您上一次访问本站的时间是：");
                    long lastLoginTime = Long.parseLong(cookie.getValue());
                    out.write(new Date(lastLoginTime).toLocaleString());
                    System.out.println(new Date(lastLoginTime).toLocaleString());
                }
            }
            if (flag) {
                out.write("这是您第一次访问本站");
            }
        }
        //服务器给客户端响应一个cookie
        Cookie cookie = new Cookie("lastLoginTime",String.valueOf(System.currentTimeMillis()));
        //cookie有效期设置为1天
        cookie.setMaxAge(24*60*60);
        resp.addCookie(cookie);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

  <servlet>
    <servlet-name>cookieDemo01</servlet-name>
    <servlet-class>com.qing.servlet.CookieDemo01</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>cookieDemo01</servlet-name>
    <url-pattern>/cookie</url-pattern>
  </servlet-mapping>
</web-app>

cookie细节

一个cookie只能保存一个信息
一个web站点能够给浏览器发送多个cookie，每一个站点最多存放20个cookie
cookie大小有限制，通常为4kb
浏览器存放cookie通常最多300

删除cookie

不设置有效期，关闭浏览器，自动失效
设置有效期为0

Session

什么是session

服务器会给每一个用户（浏览器）建立一个session对象
一个session独占一个浏览器，只要浏览器没有关闭，这个session就存在
用户登陆以后，整个网站均可以访问

session使用场景

保存登陆用户的信息
购物车信息
在整个网站中常用的数据，咱们将它保存在session中

session和cookie的区别

cookie是把要保存的数据写给浏览器，浏览器保存（能够保存多个）
session是把要保存的数据写的用户独占的session中，服务器保存（只保存重要的信息，减小服务器资源的浪费）

package com.qing.servlet;

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

public class SessionDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决中文乱码问题
        req.setCharacterEncoding("UTF-8");
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=utf-8");

        //获得session
        HttpSession session = req.getSession();

        //给session存数据
        session.setAttribute("name","清风");

        //获取session的ID
        String id = session.getId();

        //判断session是否是新建立的
        if (session.isNew()) {
            resp.getWriter().write("session建立成功，ID：" + id);
        } else {
            resp.getWriter().write("session已经在服务器中存在了，ID：" + id);
        }

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

package com.qing.servlet;

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

public class SessionDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决中文乱码问题
        req.setCharacterEncoding("UTF-8");
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=utf-8");

        //获得session
        HttpSession session = req.getSession();

        //从session中取数据
        String name = (String) session.getAttribute("name");
        System.out.println(name);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

package com.qing.servlet;

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

public class SessionDemo03 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决中文乱码问题
        req.setCharacterEncoding("UTF-8");
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=utf-8");

        //获得session
        HttpSession session = req.getSession();

        //手动注销session
        session.invalidate();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

  <servlet>
    <servlet-name>cookieDemo01</servlet-name>
    <servlet-class>com.qing.servlet.CookieDemo01</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>cookieDemo01</servlet-name>
    <url-pattern>/cookie</url-pattern>
  </servlet-mapping>
  <servlet>
    <servlet-name>sessionDemo01</servlet-name>
    <servlet-class>com.qing.servlet.SessionDemo01</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>sessionDemo01</servlet-name>
    <url-pattern>/session1</url-pattern>
  </servlet-mapping>
  <servlet>
    <servlet-name>sessionDemo02</servlet-name>
    <servlet-class>com.qing.servlet.SessionDemo02</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>sessionDemo02</servlet-name>
    <url-pattern>/session2</url-pattern>
  </servlet-mapping>
  <servlet>
    <servlet-name>sessionDemo03</servlet-name>
    <servlet-class>com.qing.servlet.SessionDemo03</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>sessionDemo03</servlet-name>
    <url-pattern>/session3</url-pattern>
  </servlet-mapping>

  <!--设置session的默认失效时间-->
  <session-config>
    <!--15分钟后session自动失效，以分钟为单位-->
    <session-timeout>15</session-timeout>
  </session-config>
</web-app>

设置session自动过时在web.xml中

<!--设置session的默认失效时间-->
<session-config>
  <!--15分钟后session自动失效，以分钟为单位-->
  <session-timeout>15</session-timeout>
</session-config>

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