Session的基本使用

1. 获取Session对象
   HttpSession session = request.getSession();`
2. Session对象功能：
   void setAttribute(String name, Object o): 存储数据到session域中
   Object getAttribute(String name): 根据key，获取值
   void removeAttribute(String name): 根据key, 删除键值对

// SessionDemo1.java 获取Session，存储数据
@WebServlet("/demo1")
public class SessionDemo1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //存储到Session中
        // 1. 获取Session对象
        HttpSession session = req.getSession();
        // 2. 存储数据
        session.setAttribute("username", "zs");
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}

// SessionDemo2 获取Session，获取所存储的数据
@WebServlet("/demo2")
public class SessionDemo2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 获取数据

        // 1. 获取Session对象
        HttpSession session = req.getSession();
        // 2. 获取数据
        Object username = session.getAttribute("username");
        System.out.println(username);

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