📄 jspadvanced5.html

📁 j2eePDF格式的电子书
💻 HTML
字号:
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">  <head>    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />    <meta http-equiv="Content-Style-Type" content="text/css" />    <title>Declarations</title>    <link rel="StyleSheet" href="document.css" type="text/css" media="all" />    <link rel="StyleSheet" href="catalog.css" type="text/css" media="all" />    <link rel="Table of Contents" href="J2EETutorialTOC.html" />    <link rel="Previous" href="JSPAdvanced4.html" />    <link rel="Next" href="JSPAdvanced6.html" />    <link rel="Index" href="J2EETutorialIX.html" />  </head>  <body>    <table width="550" summary="layout" id="SummaryNotReq1">      <tr>	<td align="left" valign="center">	<font size="-1">	<a href="http://java.sun.com/j2ee/1.4/download.html#tutorial" target="_blank">Download</a>	<br>	<a href="http://java.sun.com/j2ee/1.4/docs/tutorial/information/faq.html" target="_blank">FAQ</a>	<br>	<a href="http://java.sun.com/j2ee/1.4/docs/tutorial/information/history.html" target="_blank">History</a>	</td>        <td align="center" valign="center"><a accesskey="p" href="JSPAdvanced4.html"><img id="LongDescNotReq1" src="images/PrevArrow.gif" width="26" height="26" border="0" alt="Prev" /></a><a accesskey="c" href="J2EETutorialFront.html"><img id="LongDescNotReq1" src="images/UpArrow.gif" width="26" height="26" border="0" alt="Home" /></a><a accesskey="n" href="JSPAdvanced6.html"><img id="LongDescNotReq3" src="images/NextArrow.gif" width="26" height="26" border="0" alt="Next" /></a><a accesskey="i" href="J2EETutorialIX.html"></a>        </td>	<td align="right" valign="center">	<font size="-1">	<a href="http://java.sun.com/j2ee/1.4/docs/api/index.html" target="_blank">API</a>	<br>	<a href="http://java.sun.com/j2ee/1.4/docs/tutorial/information/search.html" target="_blank">Search</a>	<br>	<a href="http://java.sun.com/j2ee/1.4/docs/tutorial/information/sendusmail.html" target="_blank">Feedback</a></font>	</font>	</td>      </tr>    </table>    <img src="images/blueline.gif" width="550" height="8" ALIGN="BOTTOM" NATURALSIZEFLAG="3" ALT="Divider">    <blockquote><a name="wp66197"> </a><h2 class="pHeading1">Declarations</h2><a name="wp66199"> </a><p class="pBody">A <em class="cEmphasis">JSP declaration</em> is used to declare variables and methods in a page's scripting language. The syntax for a declaration is as follows: </p><div class="pPreformattedRelative"><pre class="pPreformattedRelative">&lt;%! scripting language declaration %&gt;<a name="wp66200"> </a></pre></div><a name="wp66201"> </a><p class="pBody">When the scripting language is the Java programming language, variables and methods in JSP declarations become declarations in the JSP page's servlet class.</p><a name="wp71658"> </a><h3 class="pHeading2">Initializing and Finalizing a JSP Page</h3><a name="wp71660"> </a><p class="pBody">You can customize the initialization process to allow the JSP page to read persistent configuration data, initialize resources, and perform any other one-time activities by overriding the <code class="cCode">jspInit</code> method of the <code class="cCode">JspPage</code> interface. You release resources using the <code class="cCode">jspDestroy</code> method. The methods are defined using JSP declarations.</p><a name="wp71667"> </a><p class="pBody">For example, an older version of the Duke's Bookstore application retrieved the object that accesses the bookstore database from the context and stored a reference to the object in the variable <code class="cCode">bookDBAO</code> in the <code class="cCode">jspInit</code> method.The variable definition and the initialization and finalization methods <code class="cCode">jspInit</code> and <code class="cCode">jspDestroy</code> were defined in a declaration:</p><div class="pPreformattedRelative"><pre class="pPreformattedRelative">&lt;%!private BookDBAO bookDBAO;public void jspInit() {&nbsp;&nbsp;bookDBAO =&nbsp;&nbsp;(BookDBAO)getServletContext().getAttribute(&quot;bookDB&quot;);&nbsp;&nbsp;if (bookDBAO == null)&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;Couldn't get database.&quot;);}%&gt;<a name="wp71668"> </a></pre></div><a name="wp71669"> </a><p class="pBody">When the JSP page was removed from service, the <code class="cCode">jspDestroy</code> method released the <code class="cCode">BookDBAO</code> variable.</p><div class="pPreformattedRelative"><pre class="pPreformattedRelative">&lt;%!public void jspDestroy() {&nbsp;&nbsp;bookDBAO = null;}%&gt;<a name="wp71670"> </a></pre></div>    </blockquote>   <img src="images/blueline.gif" width="550" height="8" ALIGN="BOTTOM" NATURALSIZEFLAG="3" ALT="Divider">    <table width="550" summary="layout" id="SummaryNotReq1">      <tr>	<td align="left" valign="center">	<font size="-1">	<a href="http://java.sun.com/j2ee/1.4/download.html#tutorial" target="_blank">Download</a>	<br>	<a href="http://java.sun.com/j2ee/1.4/docs/tutorial/information/faq.html" target="_blank">FAQ</a>	<br>	<a href="http://java.sun.com/j2ee/1.4/docs/tutorial/information/history.html" target="_blank">History</a>	</td>        <td align="center" valign="center"><a accesskey="p" href="JSPAdvanced4.html"><img id="LongDescNotReq1" src="images/PrevArrow.gif" width="26" height="26" border="0" alt="Prev" /></a><a accesskey="c" href="J2EETutorialFront.html"><img id="LongDescNotReq1" src="images/UpArrow.gif" width="26" height="26" border="0" alt="Home" /></a><a accesskey="n" href="JSPAdvanced6.html"><img id="LongDescNotReq3" src="images/NextArrow.gif" width="26" height="26" border="0" alt="Next" /></a><a accesskey="i" href="J2EETutorialIX.html"></a>        </td>	<td align="right" valign="center">	<font size="-1">	<a href="http://java.sun.com/j2ee/1.4/docs/api/index.html" target="_blank">API</a>	<br>	<a href="http://java.sun.com/j2ee/1.4/docs/tutorial/information/search.html" target="_blank">Search</a>	<br>	<a href="http://java.sun.com/j2ee/1.4/docs/tutorial/information/sendusmail.html" target="_blank">Feedback</a></font>	</font>	</td>      </tr>    </table>    <img src="images/blueline.gif" width="550" height="8" ALIGN="BOTTOM" NATURALSIZEFLAG="3" ALT="Divider"><p><font size="-1">All of the material in <em>The J2EE(TM) 1.4 Tutorial</em> is <a href="J2EETutorialFront2.html">copyright</a>-protected and may not be published in other workswithout express written permission from Sun Microsystems.</font>  </body></html>
⌨️ 快捷键说明

复制代码 Ctrl + C
搜索代码 Ctrl + F
全屏模式 F11
切换主题 Ctrl + Shift + D
显示快捷键 ?
增大字号 Ctrl + =
减小字号 Ctrl + -