案例需求：编写一个servlet，可以向session中存放一个消息，再编写一个servlet可以从session取得session中存放的这个消息。

案例实现：

package com.xdl.servlet;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

@WebServlet("/addSessionData.do")

public class XdlCreateSession extends HttpServlet {

    private static final long serialVersionUID = 1L;

    protected void service(HttpServletRequest request,

              HttpServletResponse response) throws ServletException, IOException {

        //如何获取session 对象

        HttpSession  session  = request.getSession();

        session.setAttribute("msg", "java是目前应用最广泛的语言");

    }

}

package com.xdl.servlet;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

@WebServlet("/getSessionData.do")

public class GetSessionDataServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    protected void service(HttpServletRequest request,

              HttpServletResponse response) throws ServletException, IOException {

        HttpSession  session = request.getSession();

        //从session 对象中获取数据

        String msg = (String)session.getAttribute("msg");

        System.out.println("msg=" + msg);

    }

}