Application
对应的类 ServletContext
用于保存整个WebApplication的生命周期内都可以访问的数据
xx extends HttpServlet
ServletContext application = this.getServletContext();
//拿到所有客户端的内存
//包括 Servlet 的整个容器
ServletContext application = this.getServletContext();
Object objValue = (Object) application.getAttribute("paramName"); application.setAttribute(" paramName ", objValue);