JavaWeb基础-8.Cookie和Session-优快云博客

本文链接：https://blog.youkuaiyun.com/u014215131/article/details/115029926

本文介绍了JavaWeb中Cookie和Session的基本概念与操作。Cookie用于在客户端存储键值对，大小有限制，服务器通过req.getCookies()获取；Session是HttpSession接口，用于维护客户端与服务器的关联，用于保存用户登录信息。创建Session使用request.getSession()，通过setMaxInactiveInterval()控制生命周期。Cookie的path属性控制发送范围，Session通过getId()获取唯一ID。

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1. Cookie饼干

1.1 什么是Cookie

Cookie是服务器通知客户端保存键值对的一种技术
客户端有了Cookie后，每次请求都发送给服务器
每个cookie大小不能超过4kb

1.2 cookie的创建

public class CookieServlet extends BaseServlet {

    protected void createCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //创建cookie对象
        Cookie cookie1 = new Cookie("key1", "value1");
        Cookie cookie2 = new Cookie("name", "gau");

        //通知客户端保存cookie
        resp.addCookie(cookie1);
        resp.addCookie(cookie2);

        resp.getWriter().write("cooke创建成功");
    }

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

1.3 服务器如何获取cookie

服务器获取客户端的cookie只需要一行代码req.getCookies().Cookie[]

获取cookie

public class CoolieUtils {
    //查找指定名称的cookie对象
    public static Cookie findCookie(String name, Cookie[] cookies) {
        if (name == null || cookies == null || cookies.length == 0) {
            return null;
        }
        for (Cookie cookie : cookies) {
            if (name.equals(cookie.getName())) {
                return cookie;
            }
        }
        return null;
    }
}

protected void getCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Cookie[] cookies = req.getCookies();
        Cookie iWantCoolie = CoolieUtils.findCookie("name", cookies);
//        for (Cookie cookie : cookies) {
//            resp.getWriter().write("cookie[" + cookie.getName() + "=" + cookie.getValue() + "]<br/>");
//            if ("name".equals(cookie.getName())) {
//                iWantCoolie = cookie;
//                break;
//            }
//        }
        //找到了需要的cookie
        if (iWantCoolie != null) {
            resp.getWriter().write("cookie find");
        }
    }

1.4 cookie值的修改

方案一：创建一个要修改的同名的cookie对象
在构造器，同时赋予新的cookie值
调用response.addCookie(cookie);

protected void updateCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Cookie cookie = new Cookie("name", "gai");
        resp.addCookie(cookie);
        resp.getWriter().write("cookie修改");
    }

方案二：先查找到需要修改的cookie对象
调用setValue()方法赋予新的cookie值
调用response.addCooike()通知客户端保存修改

    protected void updateCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Cookie cookie = CoolieUtils.findCookie("name", req.getCookies());
        if (cookie != null) {
            cookie.setValue("gei");
            resp.addCookie(cookie);
        }
    }

1.5 cookie声明控制

如何管理cookie什么时候被销毁（删除）
setMaxAge()
正值表示在指定的秒数后过期
负值表示浏览器退出，cookie删除（默认）
0表示马上删除cookie


    }

    protected void defaultLife(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Cookie cookie = new Cookie("defalutLife", "defalutLife");
        cookie.setMaxAge(-1);
        resp.addCookie(cookie);
    }

    protected void deleteNow(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Cookie cookie = CoolieUtils.findCookie("name", req.getCookies());
        if (cookie != null) {
            cookie.setMaxAge(0);//不用等待浏览器关闭马上删除
            resp.addCookie(cookie);
            resp.getWriter().write("delete cookie");
        }
    }

    protected void life(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Cookie cookie = new Cookie("life", "life");
        cookie.setMaxAge(3600);
        resp.addCookie(cookie);
        resp.getWriter().write("3600");
    }

1.6 cookie有效路径Path的设置

cookie的path属性可以有效的过滤哪些cookie可以发送给服务器，哪些不发
path属性是通过请求的地址来进行有效的过滤

CookieA path=/工程路径
CookieB path=/工程路径/abc
请求地址如下
http://ip:port/工程路径/a.html
cookieA发送 cookieB不发送
http://ip:port/工程路径/abc/a.html
cookieA发送 cookieB发送

    protected void testPath(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Cookie cookie = new Cookie("path1", "path1");
        //getContextPath()得到工程路径
        cookie.setPath(req.getContextPath() + "/abc");
        resp.addCookie(cookie);
        resp.getWriter().write("path cookie");
    }

1.7 练习：免输入用户名登录

cookie练习

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<form action="http://localhost:8080/13_cookie_session/loginServlet" method="get">
    用户名：<input type="text" name="username" value="${cookie.username.value}"><br/>
    密码：<input type="password" name="password"><br/>
    <input type="submit" value="登录">
</form>
</body>
</html>

public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        if ("gai".equals(username) && "1234".equals(password)) {
            Cookie cookie = new Cookie("username", username);
            cookie.setMaxAge(60 * 60 * 24 * 7);//cookie一周有效
            resp.addCookie(cookie);
            System.out.println("success");
        } else {
            System.out.println("failed");
        }
    }
}

2. Session会话

2.1 什么是Session会话

Session就是一个接口(HttpSession)
Session就是会话，他用来维护一个客户端和服务器之间关联的一种技术
每个客户端都有自己的一个Session会话
Session会话中，经常用来保存用户登录之后的信息

2.2 如何创建Session和获取(id号，是否为新)

request.getSession()第一次调用时创建Session会话
之后调用的是获取签名创建好的session会话对象
isNew()判断到底是不是刚创建出来的
每个会话都有一个身份证号，getId()就是ID值，而且这个ID是唯一的

public class SessionServlet extends BaseServlet {
    protected void createOrGetSession(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //创建和获取session会话对象
        HttpSession session = req.getSession();
        //判断当前session会话是否是新创建出来的
        boolean isNew = session.isNew();
        String id = session.getId();
        resp.getWriter().write("id=" + id + "<br/>isNew? " + isNew);
    }

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

2.3 Session域数据的存取

 //往session中存数据
    protected void setAttribute(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.getSession().setAttribute("key1", "value1");
    }

    //获取session中的数据
    protected void getAttribute(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Object attribute = req.getSession().getAttribute("key1");
        resp.getWriter().write("" + attribute);
    }

2.4 Session 生命周期控制

public void setMaxInactiveInterval(int interval) 设置session以秒为单位的超时时间，超过指定的时长，session就会被销毁
负值永不超时（很少使用），invalidate()马上超时无效
public int getMaxInactiveInterval() 获取session的超时时间，默认30分钟，tomcat配置文件web.xml默认以下配置
session超时是指客户端两次请求的最大间隔时长

  <session-config>
    <session-timeout>30</session-timeout>
  </session-config>

session超时

    protected void defaultLife(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        int maxInactiveInterval = req.getSession().getMaxInactiveInterval();
        resp.getWriter().write("" + maxInactiveInterval);
    }

    protected void life(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.getSession().setMaxInactiveInterval(3);
        resp.getWriter().write("3s set success");
    }

    protected void deleteNow(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.getSession().invalidate();
        resp.getWriter().write("success");
    }