JSP脚本中的9个内置对象：

application:    javax.servlet.ServletContext

config:          javax.servlet.ServletConfig

exception:     java.lang.Throwable

out:              javax.servlet.jsp.JspWriter

page:            javax.servlet.Servlet中的this

pageContext: javax.servlet.jsp.PageContext

request:        javax.servlet.http.HttpServletRequest

response:      javax.servlet.http.HttpServletResponse

session:         javax.servlet.http.HttpSession