Javaweb | 状态管理:Session、Cookie

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状态管理

问题引入

  • HTTP协议是无转态的,不能保存提交的信息
  • 如果用户发来一个新的请求,服务器无法知道它是否与上次的请求联系
  • 对于那些需要多次提交数据才能完成的web操作,比如登录,就难以完成

概念

将浏览器与web服务器之间多次交互当做一个整体来处理,并且多次交互所涉及的数据(状态)保存下来

状态管理分类

  • 客户端状态管理技术:将转态保存在客户端,代表性的是Cooklie技术
  • 服务器状态管理技术:将状态保存在服务器端,代表性的是session技术(服务器传递session时需要使用Cookie的方式)和application

Cookie

  • Cookie是浏览器访问Web服务器某个资源时,由Web服务器在HTTP响应消息头中附带传送给浏览器的小段数据
  • 一旦Web服务器保存了某个Cookie,那么它在以后每次访问该Web服务器时,都应在HTTP请求中将这个Cookie回传给Web服务器
  • 一个Cookie主要由标识该信息的名称name和值value组成

Cookie的创建、获取、修改

  • Cookie创建
@WebServlet(value = "/cs")
public class CookieServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //服务端创建Cookie对象
        Cookie cookie = new Cookie("username","weishuo");

        //设置Cookie的访问路径
        cookie.setPath("/Servlet_Projects_war/get");

        //设置Cookie的有效期  >0有效期,单位秒 =0浏览器关闭 <0内存存储  默认-1
        cookie.setMaxAge(60*60);    //1小时

        //添加到response对象中,将Cookie响应给客户端
        resp.addCookie(cookie);     //将Cookie添加到response对象中,响应给客户端

    }
}

  • Cookie获取
@WebServlet(value = "/get")
public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //通过request对象获取所有的cookie
        Cookie[] cookies = req.getCookies();
        
        if (cookies!=null){         //判断cookies数组是否为空,避免空指针异常
            //通过循环遍历Cookie
            for (Cookie cookie : cookies) {
                System.out.println(cookie.getName() + ":" + cookie.getValue());
            }
        }
        
    }

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

如果修改Cookie的name和有效路径会新建cookie,而改变Cookie值,有效期会覆盖原有的Cookie

@WebServlet(value = "/cs2")
public class CookieServlet2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //服务端创建Cookie对象
        Cookie cookie = new Cookie("username","given");

        //设置Cookie的访问路径
        cookie.setPath("/Servlet_Projects_war/get");

        //设置Cookie有效期
        cookie.setMaxAge(60*60*24*7);   //7天

        //添加到response对象中,将Cookie响应给客户端
        resp.addCookie(cookie);

    }
}

Cookie编码与解码

Cookie默认不支持中文,只能包含ASCII字符,所以Cookie需要对Unicode字符进行编码,否则会出现乱码

  • 编码可以使用java.net.URLEncoder类encode(String str,String encoding)方法
  • 解码使用java.net.URLDecoder类decode(String str,String encoding)方法
//Cookie设置

@WebServlet(value = "/cs3")
public class CookieServlet3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //服务端创建Cookie对象,使用Cookie编码
        Cookie cookie = new Cookie(URLEncoder.encode("姓名","UTF-8"),URLEncoder.encode("张三","UTF-8"));

        //设置Cookie的访问路径
        cookie.setPath("/Servlet_Projects_war/get");

        //设置Cookie有效期
        cookie.setMaxAge(600);

        //添加到response对象中,将Cookie响应给客户端
        resp.addCookie(cookie);
    }
}

//Cookie读取

@WebServlet(value = "/get")
public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //通过request对象获取所有的cookie
        Cookie[] cookies = req.getCookies();

        if (cookies!=null){         //判断cookies数组是否为空,避免空指针异常
            //通过循环遍历Cookie
            for (Cookie cookie : cookies) {
                //使用Cookie解码
                System.out.println(URLDecoder.decode(cookie.getName(),"UTF-8") + ":" + URLDecoder.decode(cookie.getValue(),"UTF-8"));
            }
        }

    }

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


总结

Cookie优点

  • 可配置到期规则
  • Cookie是一种基于文本的轻量级结构,包含简单的键值对
  • Cookie默认在过期之前是可以一直存在在客户端浏览器上

Cookie的缺点

  • 大小受到限制,浏览器对Cookie大小有4K,8K字节限制
  • 用户配置为禁用,用户禁用了浏览器或客户端接受Cookie的能力
  • Cookie可能被篡改,存在潜在风险

Session

概述

  • Session用于记录用户的状态,Session指的是一段时间,单个客户端与web服务器的一连串交互过程
  • 一个Session中,客户可能会多次请求访问同一个资源,也可能请求访问各种不同的服务器资源

原理

Tip:

Session和Cookie都是由服务器端创建

  • 服务器为每一次会话分配一个Session对象
  • 同一个浏览器发起的多次请求,同属于一次会话(Session)
  • 首次使用Session,服务器自动创建Session,并且创建Cookie存储SessionID发送回客户端

session使用

Session作用域:拥有存储数据的空间,作用范围是一次会话有效

  • 一次会话是使用同一浏览器发送到多次请求,浏览器关闭则会话结束
  • 可以将数据存入Session中,一次会话的任意位置进行获取
  • 可以传递任何数据(基本数据类型、对象、集合、数组)

获取session

//获取Session对象
HttpSession session = request.getSession();
System.out.println("id"+session.getId());	//唯一标识
package com.woniu.sessions;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;

@WebServlet(name = "Servlet", value = "/ss")
public class Servlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //通过request对象获取session对象
        HttpSession session = request.getSession();

        System.out.println(session.getId());
    }

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

Session保存数据

  • 保存数据到session中

setAttribute(属性名,Objects);

session.setAttribute("key",value);	//以键值对形式存储在session作用域中

Session获取数据

  • 获取session中数据

getAttribute(属性名);

session.getAttribute("key");	//通过String类型的key访问Object类型的value

Session移除数据

  • 从Session中删除数据

removeAttribute(属性名);

session.removeAttribute("key");		//通过移除session作用域中的值

应用

  • Servlet类
@WebServlet(name = "Servlet", value = "/ss")
public class Servlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //通过request对象获取session对象
        HttpSession session = request.getSession();

        //使用session保存数据
        session.setAttribute("username","given");


        //通过产生的session对象获取sessionId
        System.out.println(session.getId());
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}
  • GetValueServlet类
@WebServlet(name = "GetValueServlet", value = "/getValue")
public class GetValueServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        String username = (String) session.getAttribute("username");

        System.out.println("从session中获得了" + username);  //从session中获得了given

    }
}
  • RemoveServlet类
@WebServlet(name = "RemoveServlet", value = "/remove")
public class RemoveServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        session.removeAttribute("username");
    }
}
  • 结果
543D0EA33CB586691A02C00564E34CEA
从session中获得了given
从session中获得了null

Session & Request 区别

  • request是一次请求有效,请求改变,则request改变
  • session是一次会话有效,浏览器改变,则session改变
  • SessionServlet类
@WebServlet(name = "Servlet", value = "/ss")
public class SessionServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //通过request对象获取session对象
        HttpSession session = request.getSession();

        //使用session保存数据
        session.setAttribute("username","given");
        //使用request保存数据
        request.setAttribute("password",123456);
		
        //重定向跳转到/getValue
        response.sendRedirect("/Servlet_Projects_war/getValue");

        //通过产生的session对象获取sessionId
        System.out.println(session.getId());
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}
  • GetValueServlet类
@WebServlet(name = "GetValueServlet", value = "/getValue")
public class GetValueServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();

        String password = (String) request.getAttribute("password");
        System.out.println("从request中获得了" + password);

        String username = (String) session.getAttribute("username");
        System.out.println("从session中获得了" + username);  //从session中获得了given

    }
}
  • 结果
从request中获得了null
从session中获得了given

总结

sendRedirect跳转时,地址栏发生改变,代表客户端重新发送请求,属于两次请求;response没有作用域,两次request请求中的数据无法共享;而session只要浏览器不关闭属于一次会话,一次会话中浏览器数据可以共享

Session生命周期

  • 开始:第一次使用到Session的请求产生,则创建Session
  • 结束
    • 浏览器关闭,则失效
    • Session超时,则失效
      • session.SetMaxInactivelnterval(seconds); 设置最大有效时间(单位/秒)
    • 手工销毁,则失效
      • session.invalidate(); 登录退出、注销
  • LifeSessionServlet类
@WebServlet(name = "LifeSessionServlet", value = "/life")
public class LifeSessionServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取session
        HttpSession session = request.getSession();

        //设置session有效过期时间为10s
        session.setMaxInactiveInterval(10);

        //通过产生的session对象获取sessionId
        System.out.println(session.getId());
    }
}
  • GetSessionServlet类
@WebServlet(name = "GetSessionServlet", value = "/getSession")
public class GetSessionServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取session
        HttpSession session = request.getSession();

        System.out.println(session.getId());
        
        //手工销毁,立即失效
        //session.invalidate();
    }
}
  • 结果
浏览器输入/life,获取到的sessionId
71A9B2141F22840E0BE7EA67B49EC9B3

10秒内,浏览器输入/getSession,获取到的sessionId
71A9B2141F22840E0BE7EA67B49EC9B3

10秒后,浏览器输入/getSession,获取到的sessionId
EDF2E31978DE8295486C2657016F5202

浏览器禁用Cookie解决方案

浏览器禁用Cookie后果

服务器在默认情况下,会使用Cookie的方式将sessionID发送给服务器,如果用户禁止Cookie,则sessionID不会被浏览器保存,此时,服务器使用如URL重写这样的方式来发送sessionID

URL重写

浏览器在访问服务器上的某个地址时,不再使用原来的那个地址,而是使用经过改写的地址(即在原来的地址后面加上sessionID)

实现URL重写

  • response.encodeRedirectURL(String url); //生成重写的URL
//实现URL重写
String url = response.encodeRedirectURL("/Servlet_Projects_war/getSession");

//输出URL重写地址
System.out.println(url);

//重定向转发
response.sendRedirect(url);
  • 结果
重写URL地址
/Servlet_Projects_war/getSession;jsessionid=A38B1C92B9CDE10F6ED5E7AA19E919F0

浏览器输入/life,获取到的sessionId
A38B1C92B9CDE10F6ED5E7AA19E919F0

重定向转发地址:/Servlet_Projects_war/getSession,获取到的sessionId
A38B1C92B9CDE10F6ED5E7AA19E919F0
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