关于session

·cookie是把用户的数据写给用户的浏览器，让浏览器来保存（可以保存多个）

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

·session对象有服务器创建

 

session应用场景：

　　·保存一个登录用户的信息；

　　·购物车信息；

　　·在整个网站中经常会使用的数据，我们会将他保存到session中；

 

session小测试

   一·创建一个session

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

public class SessionDemo01 extends HttpServlet {

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

        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");

        //得到session
        HttpSession session = req.getSession();
        //给session中存对象
　　　　　//person是我自己创建的实体类
        session.setAttribute("Person", new Person("吴大叔",1));
        //获取sessionde ID
        String id = session.getId();
        //判断是否是新创建的
        if (session.isNew()){
            resp.getWriter().write("session创建成功，ID："+id);
        }else {
            resp.getWriter().write("已经注册sessionID："+id);
        }

        /*//session创建的时候做了什么
        Cookie cookie = new Cookie("sessionID",id);
        resp.addCookie(cookie);*/
    }

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

二·得到session中的数据

public class SessionDemo02 extends HttpServlet {

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

        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");

        //得到session
        HttpSession session = req.getSession();
        //获取name
        Person sessionAttribute = (Person) session.getAttribute("Person");

        resp.getWriter().write("获取name："+sessionAttribute);

        System.out.println(sessionAttribute);
        /*//session创建的时候做了什么
        Cookie cookie = new Cookie("sessionID",id);
        resp.addCookie(cookie);*/
    }

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

}   三·删除session

public class SessionDemo03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");

        //获取session
        HttpSession session = req.getSession();
        //=删除session中获取的数据
        session.removeAttribute("Person");
        //手动注销session，但是会形成一个新的id
        session.invalidate();
        //响应
        resp.getWriter().write("session已删除");
    }

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