JspContext对象与PageContext对象：
public abstract javax.servlet.jsp.PageContext extends (public abstract) javax.servlet.jsp.JspContext extends Object
//获取pageContext的方法
javax.servlet.jsp.JspFactory _jspxFactory = javax.servlet.jsp.JspFactory.getDefaultFactory()
pageContext = _jspxFactory.getPageContext(Servlet, ServletRequest, ServletResponse, String, boolean, int, boolean)