整理JSP九大内置对象在tomcat容器中的实际类型
（1）application实际类型：org.apache.catalina.core.ApplicationContextFacade
ApplicationContextFacade实现接口javax.servlet.ServletContext
（2）page
实际类型：org.apache.jsp.index_jsp
index_jsp继承类org.apache.jasper.runtime.HttpJspBase
HttpJspBase继承类javax.servlet.http.HttpServlet
（3）config
实际类型：org.apache.catalina.core.StandardWrapperFacade
StandardWrapperFacade实现接口javax.servlet.ServletConfig
（4）request
实际类型：org.apache.catalina.connector.RequestFacade
RequestFacade 实现接口javax.servlet.http.HttpServletRequest
（5）response
实际类型：org.apache.catalina.connector.ResponseFacade
ResponseFacade实现接口javax.servlet.http.HttpServletRequest
（6）out
实际类型：org.apache.jasper.runtime.JspWriterImpl
JspWriterImpl继承类javax.servlet.jsp.JspWriter
（7）session
实际类型：org.apache.catalina.session.StandardSessionFacade
StandardSessionFacade实现接口javax.servlet.http.HttpSession
（8）pageContext
实际类型：org.apache.jasper.runtime.PageContextImpl
PageContextImpl继承类javax.servlet.jsp.PageContext
（9）exception:
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