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📄 j-customtags-4-3.html

📁 这是用java编写自定义标签的一些源码和笔记
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<TR>
<TD bgcolor="#ffffff" height="1" width="150"><IMG src="../i/c.gif" width="150" height="1"></TD>
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<TD bgcolor="#cc6633" height="3" width="150"><IMG src="../i/c.gif" width="150" height="3"></TD>
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<TD bgcolor="#333333" height="1" width="150"><IMG src="../i/c.gif" width="150" height="1"></TD>
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<TD bgcolor="#000000" height="1" width="150"><IMG src="../i/c.gif" width="150" height="1"></TD>
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<TD bgcolor="#ffffff" height="1" width="150"><IMG src="../i/c.gif" width="150" height="2"></TD>
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<td><font size="-1" face="Verdana, sans-serif"><a href="http://www.ibm.com/">IBM</a> : <a href="/developerWorks/cn/index.shtml">developerWorks 中国网站</a> : <a href="/developerWorks/cn/java/index.shtml">Java</a> ： <a href="/developerWorks/cn/cnedu.nsf/java-onlinecourse-bytitle?OpenView&Count=50">教学 - 在线教程</a></font>
<br>
<img alt="掌握自定义 JSP 标签" src="imagemaster/masthead.jpg"></td><td width="*" valign="bottom" align="right"><a border="0" href="j-customtags.zip"><img alt="下载 ZIP 文件" border="0" src="../i/icon-zip.gif"></a><a target="_blank" href="../tutorial_eng/index.html" border="0"><img alt="英文原文" border="0" src="../i/icon-source.gif"></a>
					
					
					
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<TABLE border="0" cellpadding="0" cellspacing="0" width="100%">
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<TD width="150" height="1" bgcolor="#000000" colspan="6"><IMG alt="" height="1" width="150" src="../i/c.gif"></TD>
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<TD background="../i/sw-gold.gif"><a border="0" href="index.html" onMouseOver="iOver('topmain'); iOver('bottommain'); self.status=mainblurb; return true;" onMouseOut="iOut('topmain'); iOut('bottommain'); self.status=''; return true;"><img alt="主菜单" border="0" src="../i/main.gif" name="topmain"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topsection'); iOver('bottomsection'); self.status=sectionblurb; return true;" onMouseOut="iOut('topsection'); iOut('bottomsection'); self.status=''; return true;" href="index4.html"><img alt="章节菜单" border="0" src="../i/section.gif" name="topsection"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topfeedback'); iOver('bottomfeedback'); self.status=feedbackblurb; return true;" onMouseOut="iOut('topfeedback'); iOut('bottomfeedback'); self.status=''; return true;" href="j-customtags-7-3.html"><img alt="给出此教程的反馈意见" border="0" src="../i/feedback.gif" name="topfeedback"></a></TD><TD width="100%" background="../i/sw-gold.gif"><img src="../i/c.gif"></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topprevious'); iOver('bottomprevious'); self.status=previousblurb; return true;" onMouseOut="iOut('topprevious'); iOut('bottomprevious'); self.status=''; return true;" href="j-customtags-4-2.html"><img alt="上页" border="0" src="../i/previous.gif" name="topprevious"></a></TD><TD background="../i/sw-gold.gif"><img border="0" src="../i/xnext.gif"></TD>
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<TD colspan="5"></TD><TD align="right"><a border="0" onMouseOver="iOver('topnextsection'); iOver('bottomnextsection'); self.status=nextsectionblurb; return true;" onMouseOut="iOut('topnextsection'); iOut('bottomnextsection'); self.status=''; return true;" href="j-customtags-5-1.html"><img alt="下一章" src="../i/nextsection.gif" border="0" name="topnextsection"></a></TD>
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<table bgcolor="ffffff" cellspacing="0" cellpadding="2" border="0" height="400" width="100%">
<tr valign="bottom">
<a name="navskip"></a><td height="25" colspan="4"><img alt="4.嵌套标签" src="imagemaster/titlebar4.jpg" border="0" height="25" width="562"></td>
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<td bgcolor="ffffff" width="15">&nbsp;</td><td bgcolor="ffffff" width="12">&nbsp;</td><td valign="top" align="left" bgcolor="ffffff" width="*">
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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>用 Struts 简化自定义标签开发</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 3 页（共3 页）</nobr></font></td>
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<p>对 Struts 的深入讨论超出了本教程的范围（有关这个框架的更多信息请参阅 <a href="j-customtags-7-2.html">参考资料</a>）。不过，如果熟悉这个框架，那么这些知识会对开发自定义标签有帮助。</p>
<p>也可以不使用 Reflection，而使用 Struts 的 <code>RequestUtils</code> 实现在上一小节看到的结果，如下所示：

 

 </p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
  

 public class MapEntryTag extends TagSupport {...

 

 private String type = "java.lang.String";

 ...

 public int doEndTag() throws JspException {

     MapDefineTag mapDef = (MapDefineTag) this.getParent();

     Object objectValue = null;

     

 

 if (value !=null){

 

     if (type.equals("java.lang.String")) {

         objectValue = value;

     } else if (type.equals("java.lang.Integer")) {

         Integer intValue = Integer.valueOf(value);

         objectValue = intValue;

     } else if (type.equals("java.lang.Float")) {

         Float floatValue = Float.valueOf(value);

         objectValue = floatValue;

     }

 }else {

     /** THIS USED TO BE 30 LINES OF CODE */

     objectValue = RequestUtils.lookup(pageContext, name, property, scope);

 }

 

     mapDef.getMap().put(id,objectValue);

     return EVAL_PAGE;

 }

 

 </code>
</pre>
<p>
  

 

 可以看到，<code>objectValue = RequestUtils.lookup(pageContext, name, property, scope);</code> 这一行代替了使用 Reflection 的代码中的 30 行！ 

 Struts 自带了许多实用程序，使自定义标签的开发更容易了。

 


          </p>
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<TABLE border="0" cellpadding="0" cellspacing="0" width="100%">
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<TD background="../i/sw-gold.gif"><a border="0" href="index.html" onMouseOver="iOver('topmain'); iOver('bottommain'); self.status=mainblurb; return true;" onMouseOut="iOut('topmain'); iOut('bottommain'); self.status=''; return true;"><img alt="主菜单" border="0" src="../i/main.gif" name="bottommain"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topsection'); iOver('bottomsection'); self.status=sectionblurb; return true;" onMouseOut="iOut('topsection'); iOut('bottomsection'); self.status=''; return true;" href="index4.html"><img alt="章节菜单" border="0" src="../i/section.gif" name="bottomsection"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topfeedback'); iOver('bottomfeedback'); self.status=feedbackblurb; return true;" onMouseOut="iOut('topfeedback'); iOut('bottomfeedback'); self.status=''; return true;" href="j-customtags-7-3.html"><img alt="给出此教程的反馈意见" border="0" src="../i/feedback.gif" name="bottomfeedback"></a></TD><TD width="100%" background="../i/sw-gold.gif"><img src="../i/c.gif"></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topprevious'); iOver('bottomprevious'); self.status=previousblurb; return true;" onMouseOut="iOut('topprevious'); iOut('bottomprevious'); self.status=''; return true;" href="j-customtags-4-2.html"><img alt="上页" border="0" src="../i/previous.gif" name="bottomprevious"></a></TD><TD background="../i/sw-gold.gif"><img border="0" src="../i/xnext.gif"></TD>
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