final javax.servlet.jsp.PageContext pageContext;
javax.servlet.http.HttpSession session = null;   //仅对一次会话有效
final javax.servlet.ServletContext application;     //对于整个web应用有效,一旦jsp,servlet将数据放入application中,该数据将可以被该应用下所有jsp,servlet访问,一半用来共享数据或者读取web应用的配置参数
final javax.servlet.ServletConfig config;
javax.servlet.jsp.JspWriter out = null;
final java.lang.Object page = this;   //仅对当前页面有效
javax.servlet.jsp.JspWriter _jspx_out = null;
javax.servlet.jsp.PageContext _jspx_page_context = null;

final javax.servlet.http.HttpServletRequest request    //仅对本次请求有效
final javax.servlet.http.HttpServletResponse response

web服务器内置对象,或者说是ServletAPI的实例