java项目实践-cookie-session-day18

目录

• 1. cookie
• 2. session
• 3. servletcontext
• 4.servletConfig

1. cookie

cookie 在客户端（浏览器）中保持http状态的 信息技术

本质 是浏览器缓存

每次发请求的时候 在请求头中 带给 服务端

常见的应用场景：实现7天免登录

浏览器 F12

        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("gbk");

        Cookie cookie = new Cookie("0001", "beijing");
        response.addCookie(cookie);
        response.getWriter().write("learning cookie !");

cookie的获取

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("gbk");

        Cookie[] cookies = request.getCookies();

        if (cookies.length>0){
            for (Cookie cookie : cookies) {
                String name = cookie.getName();
                String value = cookie.getValue();

                System.out.println("key:"+ name);
                System.out.println("value:"+ value);
            }

        }

    }
}

使用之前的用户登录项目

实现7天免登录

对于之前的

loginServlet 登录成功添加cookie

//            response.getWriter().write("welcome:" + u.getName());
            Cookie cookie = new Cookie("userid", u.getId()+"");
            cookie.setMaxAge(7*24*3600);
            response.addCookie(cookie);

            response.sendRedirect("hello");

增加一个CookieServlet是实现/ck接口

package com.msb.control;

import com.msb.entity.User;
import com.msb.service.UserService;
import com.msb.service.impl.UserServiceImpl;

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.sql.SQLException;

/**
 * @Auther: jack.chen
 * @Date: 2023/10/19 - 10 - 19 - 21:07
 * @Description: ${PACKAGE_NAME}
 * @version: 1.0
 */
public class CookieServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
        this.doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("gbk");
        UserService userService = new UserServiceImpl();
        Cookie[] cookies = request.getCookies();
        if (cookies!=null){
            for (Cookie cookie : cookies) {
                String name = cookie.getName();
                if ("userid".equals(name)){
                    String userid = cookie.getValue();
                    // 对 userid 校验
                    try {
                        User u = userService.getUserById(Integer.valueOf(userid));
                        if (u!=null){
                            response.sendRedirect("hello");
                        }else{
                            response.sendRedirect("page");
                        }
                    } catch (SQLException e) {
                        e.printStackTrace();
                    } catch (ClassNotFoundException e) {
                        e.printStackTrace();
                    }
                    return;

                }
            }
                response.sendRedirect("page");
        }else{
            response.sendRedirect("page");
        }

    }
}

/ck-->/page 未登录

/ck --> /hello 已经登录

2. session

登录成功之后 再访问其他的页面 不需要再带上 用户名密码 就能直接访问

现实的例子：理发店 办理会员卡

第一种方式：给客户留一张 卡片--客户端

第二种方式：之后只要 报卡号 或者手机号--服务端

session是用于解决用户访问不同页面时 带上sessionid

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("sess api do get ");
        HttpSession session = request.getSession();
        System.out.println("session id:"+session.getId());

        response.getWriter().write("learn session");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");

        response.setContentType("text/html:charset=utf-8");

        System.out.println("sess api do get ");
        HttpSession session = request.getSession();
        System.out.println("session id:"+session.getId());

        //设置有效期
//        session.setMaxInactiveInterval(5);
        // 强制失效
//        session.invalidate();

        session.setAttribute("111", "beijing");
        response.getWriter().write("learn session");
    }

        Object attribute = (String)session.getAttribute("111");
        response.getWriter().write("get session attr:"+attribute);

实现登录页面 欢迎xxxx登录

            HttpSession session = request.getSession();
            session.setAttribute("name", u.getName());

        HttpSession session = request.getSession();
        String name = (String)session.getAttribute("name");

3. servletcontext

不同用户 数据传递 数据共享 ---当前访问人数 当前帖子的的在线阅读人数



被web项目中所有的servlet访问

服务器创建 一个项目只能有一个servletcontext对象

项目的任意位置 获取到的是同一个对象

该对象所有用户共有

servlet1

        ServletContext servletContext = this.getServletContext();
//        ServletContext servletContext = this.getServletConfig().getServletContext();
//        ServletContext servletContext = request.getSession().getServletContext();
        //三种方式获取的都是同一个对象

        servletContext.setAttribute("111", "beijing");
        response.getWriter().write("servlet context 1");

servlet2

        ServletContext servletContext = this.getServletContext();

        String attribute = (String)servletContext.getAttribute("111");

        System.out.println(attribute);
        response.getWriter().write("servlet context 2");

公共设置

web.xml中的公共配置

    <context-param>
        <param-name>beijing</param-name>
        <param-value>beautiful</param-value>
    </context-param>

        String beijing = (String)servletContext.getInitParameter("beijing");
        System.out.println(beijing);

如何实现 当前访问量的统计

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");

        ServletContext context = this.getServletContext();
        Integer num = (Integer) context.getAttribute("num");
        if(num==null){
            context.setAttribute("num", 1);
        }else{
            num++;
            context.setAttribute("num", num);
        }
        PrintWriter writer = response.getWriter();
        writer.write("<html>");
        writer.write("<head>");
        writer.write("</head>");
        writer.write("<body>");
        writer.write("用户访问量："+context.getAttribute("num"));
        writer.write("</body>");
        writer.write("</html>");

    }

4.servletConfig

每个servlet 单独获取自己的属性配置

        ServletConfig servletConfig = this.getServletConfig();
        String china = servletConfig.getInitParameter("china");
        System.out.println("====="+china+"==");