Session方法
invalidate() 就是从session对象池中删除session
isNew() boolean； true刚刚创建的Session；false 不是新建的Session
session本地持久化

                      只要正常途径关闭tomcat服务器 就会把session内容存储到本地
                      注意，如果你在session存放对象，那这个对象想存储在磁盘上必须实现接口 java.io.Serializable

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/hello")
public class B extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        Test test = new Test();
        test.setName("小明");
        session.setAttribute("Test", test);//通过对象的方式存储
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("a");
        requestDispatcher.forward(request, response);
    }
}
----

package com.sun.tomcat;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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.io.PrintWriter;
import javax.servlet.http.HttpSession;

@WebServlet("/a")
public class A extends HttpServlet {

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        Test test = (Test) session.getAttribute("Test"); //将对象进行强制类型转化
        System.out.println(test.getName());//用转换后的对象进行取值
    }
}
----
package com.sun.tomcat;

import java.io.Serializable;

public class Test implements Serializable {//实现序列化技术
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Test{" +
                "name='" + name + '\'' +
                '}';
    }


}