前言

jsp本质上是一个servlet，而在jsp中有九个不用声明就可以使用的对象，我们叫他隐含对象。本文基于上文所写，如有需要可查看上一篇文章javaWEB总结(11):JSP简介及原理.

打开上次使用的login_jsp.java文件

    /*

     * Generated by the Jasper component of Apache Tomcat

     * Version: Apache Tomcat/7.0.54

     * Generated at: 2016-11-26 07:51:43 UTC

     * Note: The last modified time of this file was set to

     *       the last modified time of the source file after

     *       generation to assist with modification tracking.

     */

    package org.apache.jsp;  

    import javax.servlet.*;

    import javax.servlet.http.*;

    import javax.servlet.jsp.*;  

    public final class login_jsp extends org.apache.jasper.runtime.HttpJspBase

        implements org.apache.jasper.runtime.JspSourceDependent {  

      private static final javax.servlet.jsp.JspFactory _jspxFactory =

              javax.servlet.jsp.JspFactory.getDefaultFactory();  

      private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;  

      private javax.el.ExpressionFactory _el_expressionfactory;

      private org.apache.tomcat.InstanceManager _jsp_instancemanager;  

      public java.util.Map<java.lang.String,java.lang.Long> getDependants() {

        return _jspx_dependants;

      }  

      public void _jspInit() {

        _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();

        _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());

      }  

      public void _jspDestroy() {

      }  

      public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)

            throws java.io.IOException, javax.servlet.ServletException {  

        final javax.servlet.jsp.PageContext pageContext;

        javax.servlet.http.HttpSession session = null;

        final javax.servlet.ServletContext application;

        final javax.servlet.ServletConfig config;

        javax.servlet.jsp.JspWriter out = null;

        final java.lang.Object page = this;

        javax.servlet.jsp.JspWriter _jspx_out = null;

        javax.servlet.jsp.PageContext _jspx_page_context = null;  

        try {

          response.setContentType("text/html; charset=utf-8");

          pageContext = _jspxFactory.getPageContext(this, request, response,

                    null, true, 8192, true);

          _jspx_page_context = pageContext;

          application = pageContext.getServletContext();

          config = pageContext.getServletConfig();

          session = pageContext.getSession();

          out = pageContext.getOut();

          _jspx_out = out;  

          out.write("\r\n");

          out.write("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\r\n");

          out.write("<html>\r\n");

          out.write("<head>\r\n");

          out.write("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=ISO-8859-1\">\r\n");

          out.write("<title>my first jsp</title>\r\n");

          out.write("</head>\r\n");

          out.write("<body>\r\n");

          out.write("\t");

     out.write("Hello World") ;

          out.write("\r\n");

          out.write("</body>\r\n");

          out.write("</html>");

        } catch (java.lang.Throwable t) {

          if (!(t instanceof javax.servlet.jsp.SkipPageException)){

            out = _jspx_out;

            if (out != null && out.getBufferSize() != 0)

              try { out.clearBuffer(); } catch (java.io.IOException e) {}

            if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);

            else throw new ServletException(t);

          }

        } finally {

          _jspxFactory.releasePageContext(_jspx_page_context);

        }

      }

    }

我们只看下面这段代码

  public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)

        throws java.io.IOException, javax.servlet.ServletException {

    //参数中定义了两个隐含变量 request和 response

    //下面定义了六个隐含变量   pageContext,session,application,config,out,page

   final javax.servlet.jsp.PageContext pageContext;

    javax.servlet.http.HttpSession session = null;

    final javax.servlet.ServletContext application;

    final javax.servlet.ServletConfig config;

    javax.servlet.jsp.JspWriter out = null;

    final java.lang.Object page = this;

	//…………………………

	//<%%>中的代码

	//…………………………

 }

可以看到共有八个隐含对象

(1) request: HttpServletRequest的一个对象；

(2) response: HttpServletResponse的一个对象；(页面中几乎不用)

(3) pageContext: 页面的上下文，是PageContext的一个对象，可以从中获取其他8个隐含对象，也可以从中获取当前页面的其他信息(可参考如下API中PageContext对象的方法)；(自定义标签时使用)

Method Summary
`abstract void`	`forward(String relativeUrlPath)` This method is used to re-direct, or "forward" the current ServletRequest and ServletResponse to another active component in the application.
`ErrorData`	`getErrorData()` Provides convenient access to error information.
`abstract Exception`	`getException()` The current value of the exception object (an Exception).
`abstract Object`	`getPage()` The current value of the page object (In a Servlet environment, this is an instance of javax.servlet.Servlet).
`abstract ServletRequest`	`getRequest()` The current value of the request object (a ServletRequest).
`abstract ServletResponse`	`getResponse()` The current value of the response object (a ServletResponse).
`abstract ServletConfig`	`getServletConfig()` The ServletConfig instance.
`abstract ServletContext`	`getServletContext()` The ServletContext instance.
`abstract HttpSession`	`getSession()` The current value of the session object (an HttpSession).
`abstract void`	`handlePageException(Exception e)` This method is intended to process an unhandled 'page' level exception by forwarding the exception to the specified error page for this JSP.
`abstract void`	`handlePageException(Throwable t)` This method is intended to process an unhandled 'page' level exception by forwarding the exception to the specified error page for this JSP.
`abstract void`	`include(String relativeUrlPath)` Causes the resource specified to be processed as part of the current ServletRequest and ServletResponse being processed by the calling Thread.
`abstract void`	`include(String relativeUrlPath, boolean flush)` Causes the resource specified to be processed as part of the current ServletRequest and ServletResponse being processed by the calling Thread.
`abstract void`	`initialize(Servlet servlet,ServletRequest request,ServletResponse response, String errorPageURL, boolean needsSession, int bufferSize, boolean autoFlush)` The initialize method is called to initialize an uninitialized PageContext so that it may be used by a JSP Implementation class to service an incoming request and response within it's _jspService() method.
`BodyContent`	`pushBody()` Return a new BodyContent object, save the current "out" JspWriter, and update the value of the "out" attribute in the page scope attribute namespace of the PageContext.
`abstract void`	`release()` This method shall "reset" the internal state of a PageContext, releasing all internal references, and preparing the PageContext for potential reuse by a later invocation of initialize().

(4) session: 代表游览器和服务器的一次会话，是HttpSession的一个对象；

(5) application: 代表当前web应用，是ServletContext的一个对象；

(6) config: 当前jsp对应的servlet的ServletConfig对象，需要访问当前jsp配置的初始化参数(如下)；(几乎不使用)

<servlet>

        <servlet-name></servlet-name>

        <jsp-file>

            <!-- 与java文件不同在于此标签，填写jsp文件的具体路径

                                    ，如WebContent下的index.jsp

                                    则填写/index.jsp

            -->

        </jsp-file>

    </servlet>

    <servlet-mapping>

        <servlet-name></servlet-name>

        <url-pattern></url-pattern>

    </servlet-mapping>

(7) out: JspWriter的一个对象，调用out.println()可以直接将字符串打印到游览器上；

(8) page: 指向当前JSP对应的Servlet对象的引用，但为Object类型，只能调用Object对象的方法;(几乎不使用)

第九个隐含对象

exception:在声明了page指令的isErrorPage="true"时才可以使用(如下);

<%@ page language="java" contentType="text/html; charset=utf-8"

	pageEncoding="utf-8"%>

<!-- 此处声明了page的isErrorPage	 -->

<%@ page isErrorPage="true" %>	

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">

<title>my first jsp</title>

</head>

<body>

	<% out.write("Hello World") ;

	exception.getMessage();

	%>

</body>

</html>

作用域范围

pageContext--> request--> session--> application 对属性的作用域从小到大。

javaWEB总结(12):JSP页面的九个隐含对象的更多相关文章

jsp上的九个隐含对象
首先说一说件jsp的原理.jsp被认为最经典的解释是 “嵌入了java 代码的html”. 在网上查了一些资料,和我本身对jsp的认识,总结如下: jsp本质上是一个servlet,继承自当第一次 ...
JSP数据交互——九大内置对象及其方法详解（一）
①既然说到JSP内置对象,那么什么是JSP内置对象呢? 解析:JSP内置对象,就是在编写JSP页面时,不需要做任何声明就可以直接使用的对象. 如下代码片段: <% int[] value ...
javaweb之jsp的九个隐含对象与基本语法
1.在页面上可以不用声明直接使用的对象称为jsp页面的隐含对象.使用<% %>编写的java代码在_jspService方法中,如下: public void _jspService(fi ...
【JavaWEB SSH】jsp页面传值后台Controller 部分值绑定不上实体类
//前端ajax代码 1 var oldpassword = $('#old_password').val(); var password = $('#L_pass').val(); var user ...
JSP中的九大内置对象
JSP九大内置对象 pageContext 存东西 Request 存东西 Response Session 存东西 Application(servletContext) 存东西 config(se ...
jsp页面元素和内置对象
java server pages其根本是一个简化的servlet设计.实现了在java当中使用html标签.javaEE标准一.页面元素 1.静态内容 html.js.css相关标签元素. 2.指 ...
Jsp的九个隐含对象
JSP的9个隐含对象(内置对象) 不需要预先声明,就可以在jsp或者表达式中随意使用 out javax.servlet.jsp.JspWriter类型,代表输出流的对象.作业域:页面的执行期. re ...
EL表达式的语法介绍及九大隐含对象
一. 简介 > JSP表达式 <%= %> 用于向页面中输出一个对象. > 到JSP2.0时,在我们的页面中不允许出现 JSP表达式和脚本片段. > 使用EL表达式来代 ...
Idea中JSP页面中out内置对象报错out.println标红问题
问题如图: 解决方法: 导入jar包 1.在pom.xml的<dependencies>里面复制 <dependency> <groupId>javax.servl ...

随机推荐

JSP标签<meta>的作用
meta标签: meta标签共有两个属性,它们分别是http-equiv属性和name属性. name 属性 :<meta name="Generator" contect= ...
[转载]关于shell脚本的基本语法
关于shell脚本的基本语法整理于:2014-03-31,何俭飞,mymladdr@sina.com 一.执行 1.shell脚本如果要被执行,一般地必须要有执行权限"x"(除了 ...
maven插件报错之解决
maven插件报错之解决用m2eclipse创建Maven项目时报错 maveneclipsebuilddependenciesauthorizationplugins 用m2eclipse创建 ...
linux 查看磁盘占用情况
查看"/usr/local/"路径下,所有文件大小总和.只列出总和,不显示该路径下各子文件的大小. du -sh /usr/local/ 结果显示如下图: 如果要详细显示出各子文件 ...
centos搭建svn服务器
1.在centos6.5上面搭建svn服务器,安装svn服务器:yum install subversion 2.在任意目录下创建仓库目录,这里放在/data/mypros目录下 3.执行命令:svn ...
Javac编译与JIT编译
本文转载自:http://blog.csdn.net/ns_code/article/details/18009455 编译过程不论是物理机还是虚拟机,大部分的程序代码从开始编译到最终转化成物理机的 ...
linux命令之ifconfig详细解释
依赖于ifconfig命令中使用一些选项属性,ifconfig工具不仅可以被用来简单地获取网络接口配置信息,还可以修改这些配置. 1．命令格式: ifconfig [网络设备] [参数] 2．命令功能 ...
Symfony没有安装依赖_PHP Fatal error: require(): Failed opening required
$ php bin/console server:run PHP Warning: require(D:\home\workspace\pd\app/../vendor/autoload.php): ...
JavaScriptSerializer返回一条Json，页面获取值问题，数据绑定
一,后台处理数据方法 JavaScriptSerializer serializer = new JavaScriptSerializer(); string js = serializer.Seri ...
【1】JavaScript编程全解笔记（一）
1.概述本书涵盖了 JavaScript 各个方面的主题,从客户端以及服务端 JavaScript 等基础内容,主要讲了 HTML5.Web API.Node.js 与 WebSocket 等技术 ...

javaWEB总结(12):JSP页面的九个隐含对象

前言