Cookie&Seesion

Cookie&Seesion

​ Seesion (会话)：用户打开浏览器，点击网页，访问web资源，关闭浏览器的过程

​ 有状态的会话：带Cookie的访问

Cookie讲解

​ 客户端技术 ->响应、请求

​ 从请求中拿到Cookie信息

​ 服务器响应给客户端

相关方法

public Cookie(String name, String value) //构方
Cookie[] getCookies() //获取Cookie
getName		//获取cookie的key
getValue	//获取cookie的value
setMaxAge(int expiry) //设置cookie的有效期

eg：

​ 获取上一次访问的时间

class

//获取上一次访问的时间
public class ServletDemo extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //处理中文乱码
        resp.setContentType("text/html");
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");

        PrintWriter out = resp.getWriter();

        //服务端 从客户端获取Cookie
        Cookie[] cookies = req.getCookies(); //此处返回数组，则说明Cookie可能存在多个

        //判断Cookie是否存在
        if (cookies != null){
            out.write("上一次访问的时间为：");

            for (int i = 0; i < cookies.length; i++) {
                Cookie cookie = cookies[i];
                //获取Cookie名 并进行判断
                if (cookie.getName().equals("lastTime")){
                    long l = Long.parseLong(cookie.getValue());
                    Date date = new Date(l);
                    out.write(date.toLocaleString());
                }
            }
        }else {
            out.write("第一次访问");
        }
        //服务器为客户端响应Cookie
        Cookie cookie = new Cookie("lastTime", System.currentTimeMillis() + "");

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

        resp.addCookie(cookie);
    }

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

web.xml

<?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>cookieDemo</servlet-name>
        <servlet-class>com.rz.servlet.ServletDemo</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>cookieDemo</servlet-name>
        <url-pattern>/cookie</url-pattern>
    </servlet-mapping>

</web-app>

Session

​ 服务器技术->将信息和数据存在于Seeion中

​

​ 服务器将会为每一个用户(浏览器)创建Session。只要浏览器未关闭，则Session便存在。

​ eg：B站登陆时，若你选择记住我后。再次登陆时，B站自动登录你的账号。

class

/*
    Session创建时，过程：
        resp.addCookie(new Cookie("JSESSIONID",sessionId);
 */
public class ServletDemo extends HttpServlet {

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

        //得到Session
        HttpSession session = req.getSession();

        //给Session中存东西
        session.setAttribute("name","Tom");

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

        //判断该Seesion是否为新的
        if (session.isNew()){
            resp.getWriter().write("session创建成功 "+id);
        }else {
            resp.getWriter().write("session已存在 "+id);
        }

    }

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

​ web.xml

<?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>sessionDemo</servlet-name>
        <servlet-class>com.rz.servlet.ServletDemo</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>sessionDemo</servlet-name>
        <url-pattern>/session</url-pattern>
    </servlet-mapping>

</web-app>

session和cookie的区别

Cookie是把用户的数据写给用户的浏览器，由浏览器保存

Seesion把用户的数据写到用户独占的Session中，服务端保存（保存重要信息，减少服务器资源的浪费）

Session对象由服务器创建