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From Barney Hamish <Hamish.Bar...@ect-telecoms.de>
Subject RE: Could this be a Tag Libs implementation bug?
Date Tue, 04 Feb 2003 11:09:53 GMT
Have you considered using the struts logic tags
(http://jakarta.apache.org/struts/index.html) or the JSTL
(http://jakarta.apache.org/taglibs/index.html) rather than implementing this
stuff yourself? There are some useful custom tags (like the iterate tag
you're trying to implement).
Hamish

> -----Original Message-----
> From: Switch [mailto:switch2002es@yahoo.es]
> Sent: Tuesday, February 04, 2003 11:10 AM
> To: Tomcat User Group
> Subject: Could this be a Tag Libs implementation bug?
> 
> 
> Hello everybody.
> 
> I've just signed up this list, then I must present myselft first.
> My name is Paco. I'm a J2EE developer for a local SW copany 
> at Balearic
> Islands (Spain - Europe).
> 
> I apologize me for my english. I write as well as I can :-)
> I've read the etiquette and I've read the FAQ and I've read the mail
> archieve, without having found an explanation to my problem.
> 
> Here it goes:
> 
> I've developed a small "iterate" TagLib. This Tag Lib works 
> fine with WL and
> Oracle iAS and I'm currently migrating to jboss + tomcat.
> 
> At the end of this e-mail I'will paste some code to explain 
> properly why I
> think there's a bug.
> I've created a very simple JSP that tests my "IterateTag" and I get a
> "NullPointerException" because of the EVAL_BODY_INCLUDE returned by
> doStartTag.
> 
> I've been looking ".java" generated file from ".jsp" and I 
> can see this
> piece of code:
> 
>  int _jspx_eval_bit_iterate_0 = _jspx_th_bit_iterate_0.doStartTag();
>  if (_jspx_eval_bit_iterate_0 != 
> javax.servlet.jsp.tagext.Tag.SKIP_BODY) {
>    String str = null;
>    if (_jspx_eval_bit_iterate_0 !=
> javax.servlet.jsp.tagext.Tag.EVAL_BODY_INCLUDE) {
>      javax.servlet.jsp.tagext.BodyContent _bc = 
> pageContext.pushBody();
>      _bc.clear();
>      out = _bc;
>      _jspx_th_bit_iterate_0.setBodyContent(_bc);
>      _jspx_th_bit_iterate_0.doInitBody();
>      str = (String) pageContext.findAttribute("str");
>    }
>    do {
>      ...
>      if (evalDoAfterBody !=
> javax.servlet.jsp.tagext.BodyTag.EVAL_BODY_AGAIN)
>        break;
>    } while (true);
>    if (_jspx_eval_bit_iterate_0 !=
> javax.servlet.jsp.tagext.Tag.EVAL_BODY_INCLUDE)
>      out = pageContext.popBody();
>  }
> 
> I can't undestand why this generated ".java" file executes "if !=
> EVAL_BODY_INCLUDE" and I think it should be "if == 
> EVAL_BODY_INCLUDE" (May
> be I'm wrong).
> 
> I've read the following at J2EE 1.3 javadoc about BodyTagSupport class
> (http://java.sun.com/j2ee/sdk_1.3/techdocs/api/javax/servlet/j
> sp/tagext/Tag.
> html#EVAL_BODY_INCLUDE):
> 
> EVAL_BODY_INCLUDE
> public static final int EVAL_BODY_INCLUDE
> 
> Evaluate body into existing out stream. Valid return value 
> for doStartTag
> 
> I can workarround this by returning EVAL_BODY_BUFFERED (so 
> this isn't a
> critical error)
> 
> Could anybody explain why is _jspx_eval_bit_iterate_0 being 
> compared to be
> not EVAL_BODY_INCLUDE?
> 
> Tell me if you need something else.
> 
> Thanks in advance for your help.
> 
> 
> Some source code for "ItareateTag.java"
> ---
> public int doStartTag() throws JspTagException
>   {
>     if(iterator==null) return SKIP_BODY;
>     if(iterator.hasNext())
>     {
>       
> pageContext.setAttribute(name,iterator.next(),PageContext.PAGE_SCOPE);
>       Enumeration en =
> pageContext.getAttributeNamesInScope(PageContext.PAGE_SCOPE);
>       while (en.hasMoreElements()) 
> System.out.println("Attributute: " +
> en.nextElement());
>       return EVAL_BODY_INCLUDE;
>     }
>     else return SKIP_BODY;
>   }
> 
>   public int doAfterBody() throws JspTagException
>   {
>     System.out.println("IterateTag.doAfterBody. name: " + name + "
> Iteratior: " + iterator + "Type: " + type);
>     if(iterator.hasNext())
>     {
>       
> pageContext.setAttribute(name,iterator.next(),PageContext.PAGE_SCOPE);
>       return EVAL_BODY_AGAIN;
>     }
>     else
>     {
>       return SKIP_BODY;
>     }
>   }
> 
>   public int doEndTag() throws JspTagException
>   {
>     System.out.println("IterateTag.doEndTag. name: " + name + 
> " Iteratior: "
> + iterator + "Type: " + type);
>     try
>     {
>       if(bodyContent != null)
>         bodyContent.writeOut(bodyContent.getEnclosingWriter());
>     }
>     catch(java.io.IOException e)
>     {
>       throw new JspTagException("IO Error: " + e.getMessage());
>     }
>     System.out.println("Fin IterateTag.doEndTag. ");
>     return EVAL_PAGE;
>   }
> ---
> 
> Some source code for a JSP test file:
> ---
> <%@ page contentType="text/html;charset=ISO-8859-15"%>
> <%@ page import="java.util.*" %>
> <%@ taglib uri="mytags" prefix="bit" %>
> <%
>   Vector v = new Vector();
>   v.addElement("First Element");
>   v.addElement("Second Element");
>   v.addElement("Third Element");
>   v.addElement("Fourth Element");
> %>
> <html>
>   <head></head>
>   <body>
>     <table>
>       <bit:iterate name="str" collection="<%=v%>" type="String">
>         <tr><td>This items contains <%=str.length()%> 
> characters and its
> value is <%=str%></td></tr>
>       </bit:iterate>
>     </table>
> </body>
> ---
> 
> taglib.tld contents:
> ---
> <?xml version="1.0" encoding="ISO-8859-1" ?>
> <!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP 
> Tag Library
> 1.1//EN" "http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1.dtd">
> <taglib>
> 	<tlibversion>1.0</tlibversion>
> 	<jspversion>1.1</jspversion>
> 	<shortname>test</shortname>
> 	<uri></uri>
> 	<info>Iterate Tag Lib.</info>
>       <tag>
> 		<name>iterate</name>
> 		<tagclass>es.caib.dembs.tags.IterateTag</tagclass>
> 		<teiclass>es.caib.dembs.tags.IterateTEI</teiclass>
> 		<bodycontent>JSP</bodycontent>
> 		<info>a simple iterator</info>
> 		<attribute>
> 			<name>collection</name>
> 			<required>true</required>
> 			<rtexprvalue>true</rtexprvalue>
> 		</attribute>
> 		<attribute>
> 			<name>name</name>
> 			<required>true</required>
> 		</attribute>
> 		<attribute>
> 			<name>type</name>
> 			<required>true</required>
> 		</attribute>
> 	</tag>
> </taglib>
> ---
> 
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