JSP内置对象application、out、page、config，exception总结(五)

来源：互联网发布：java配置log4j 编辑：程序博客网时间：2024/05/29 11:33

(一).application对象常用方法：
https://docs.oracle.com/javaee/7/api/javax/servlet/ServletContext.html

1.使用application获取指定页面的路径

<%@ page language="java" contentType="text/html; charset=utf-8"    pageEncoding="utf-8"%><!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=utf-8"><title>Insert title here</title></head><body>     <center>           <h3>指定实际路径、相对路径、应用程序当前路径</h3>           </h>           <table border="1" bordercolor="black">               <tr>                   <td>服务器名称和版本</td>                   <td>index.jsp页面实际路径</td>                   <td>index.jsp的URL</td>                   <td>当前Web程序路径</td>               </tr>               <tr>                    <td><%=application.getServerInfo()%></td>                    <td><%=application.getRealPath("index.jsp") %></td>                    <td><%=application.getResource("index.jsp") %></td>                    <td><%=application.getContextPath()%></td>               </tr>           </table>     </center></body></html>

输出：

这里写图片描述

2.使用application保存网站访问人数，使得多个JSP，Servlet共享数据

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%    Integer count =(Integer) application.getAttribute("count");    if(count==null){        count=1;    }else{        count++;    }    application.setAttribute("count",count); %><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>网站计数器</title>  </head>  <body>  <center>       欢迎访问本网站，您是第<%=count %>位访问客户！      </center>  </body></html>

输出：

这里写图片描述

(二)out对象

1.out对象是Java.servlet.jsp.JspWriter类的实例

2.out对象常用方法：
https://tomcat.apache.org/tomcat-4.1-doc/servletapi/javax/servlet/jsp/JspWriter.html

3.实例演示

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>演示out对象</title>  </head>  <body>     <center>         <hr>         <h4>以下就是一个表格</h4>         <%            out.println("<table border='2'>");            out.println("<tr>");            out.println("<td width='60'>"+"姓名"+"</td>");            out.println("<td width='40'>"+"性别"+"</td>");            out.println("<td width='80'>"+"出生年月"+"</td>");            out.println("<td width='60'>"+"城市"+"</td>");            out.println("</tr>");            out.println("<tr>");            out.println("<td width='60'>"+"Smith"+"</td>");            out.println("<td width='60'>"+"Male"+"</td>");            out.println("<td width='60'>"+"1984.8"+"</td>");            out.println("<td width='60'>"+"NerYork"+"</td>");            out.println("</tr>");            out.println("</table>");          %>     </center>  </body></html>

输出：
这里写图片描述

(三)page对象

1.page对象就是Java.lang.Object对象

2.常用方法：https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html

3.实例演示

 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>演示page对象</title>  </head>  <body>  <center>      <%         int code = page.hashCode();          String str = page.toString();         out.println("page对象的hash码:"+code+"&nbsp;&nbsp;</br>");         out.println("page对象的值:"+str);      %>      </center>  </body></html>

输出：
这里写图片描述

(四)config对象

1.config对象是javax.servlet.ServletConfig类的实例

2.常用方法：
https://docs.oracle.com/javaee/6/api/javax/servlet/ServletConfig.html

3.实例演示：

<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5"     xmlns="http://java.sun.com/xml/ns/javaee"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee     http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">  <welcome-file-list>    <welcome-file>index.jsp</welcome-file>  </welcome-file-list>  <servlet>      <servlet-name>           jspconfigdemo       </servlet-name>       <jsp-file>/index.jsp</jsp-file>       <init-param>           <param-name>url</param-name>           <param-value>http://www.baidu.com</param-value>       </init-param>  </servlet>  <servlet-mapping>      <servlet-name>            jspconfigdemo      </servlet-name>      <url-pattern>/index.jsp</url-pattern>  </servlet-mapping></web-app>---------- <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>演示config对象</title>  </head>  <body>     <%         String url = config.getInitParameter("url");         String str = config.toString();         out.print("page对象的initParameter方法："+url+"</br>");         out.print("page对象的toString方法："+str);      %>  </body></html>

输出：

这里写图片描述

(五)exception对象的使用

说明：JPS异常处理机制，实际上就是Java异常处理机制

1.exception处理页面异常的方法

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8" errorPage="error.jsp" %><!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=UTF-8"><title>JSP脚本异常</title></head><body>   <%      int a=8;      int b=0;      int c=a/b;             %></body></html>

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"  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=UTF-8"><title>异常处理页面</title></head><body> <hr>   异常类型：<%=exception.getClass() %><br/><br/>   异常信息： <%=exception.getMessage() %> <hr>  </body></html>

做法是：1.<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8" errorPage="error.jsp" %>2.<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"  isErrorPage="true"%>

输出结果：

这里写图片描述

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