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From "Karr, David" <david.k...@attws.com>
Subject RE: Cooperating tag
Date Tue, 31 Dec 2002 19:33:42 GMT
In the Struts source distribution, look at:

contrib/struts-el/src/share/org/apache/strutsel/taglib/html/ELButtonTag.java

Look at the "evalAttr()" and "evaluateExpressions()" methods, and the "EvalHelper" utility
class.  The latter is what calls the EL evaluator.

Also note that you may have to write BeanInfo classes if one or more of your tag attributes
are not of type String.  Look at ELButtonTagBeanInfo.java for an example of that.

> -----Original Message-----
> From: Randy Belknap [mailto:randy.belknap@thrasys.com]
> 
> Can you point me to a particular file that shows what you are 
> talking about?
> I've looked through both the tags in the distribution and 
> CVS, but haven't
> found an example.
> 
> Thanks!
> 
> > -----Original Message-----
> > From: Karr, David [mailto:david.karr@attws.com]
> > 
> > In JSP 1.2, you have to specifically use the API for the JSTL 
> > expression language engine if you want attributes to use the 
> > "${...}" syntax.  In JSP 2.0, this will happen automagically, 
> > but we're not there yet.
> > 
> > If you want one example of how this is done, look at the 
> > Struts-EL contrib library, which is part of the Struts 
> > distribution.  You'll find that the Tag classes pass the 
> > attribute values through the EL to generate the final value.
> > 
> > > -----Original Message-----
> > > From: Randy Belknap [mailto:randy.belknap@thrasys.com]
> > > 
> > > Should I be able to create a variable using <c:set> and then 
> > > use it to set
> > > the value of an attribute in my own custom tag? 
> > > 
> > > When I try and use "${myVar}" to pass the value to my 
> > custom tag, what
> > > receive is the literal "${myVar}".  In otherwords it doesn't 
> > > evaluate the
> > > expression.  I've tested under Tomcat 4.0.6, 4.1.17 and 4.1.18.
> > > 
> > > I've created the smallest possible test case and am including 
> > > all the files.
> > > 
> > > 
> > > Thanks,
> > > 
> > > Randy
> > > 
> > > === JSP PAGE ===
> > > <%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>
> > > <%@ taglib prefix="x" uri="http://java.sun.com/jstl/xml" %>
> > > <%@ taglib uri="portaltags" prefix="xe" %>
> > > <html><body>
> > > 
> > > <c:set var="myVar" scope="page" value="1"/>
> > > 
> > > <p><xe:MsgType messageType="${myVar}"/>
> > > 
> > > </body></html>
> > > 
> > > === The taglib.tld ===
> > > <?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>1.2</jspversion>
> > >    <shortname>xe</shortname>    
> > >    <uri>http://www.test.com/portaltags.html</uri>    
> > >    <info>XePortal</info>
> > >     
> > >    <tag>        
> > >     <name>MsgType</name>
> > >     <tagclass>com.test.XeTestTag</tagclass>
> > >     <info>Gets message types</info>
> > >        <attribute>
> > >          <name>messageType</name>
> > >          <required>true</required>
> > >          <rtexprvalue>true</rtexprvalue>
> > >        </attribute>
> > >     </tag>
> > > </taglib>
> > > 
> > > === The web.xml ===
> > > <?xml version="1.0" encoding="ISO-8859-1"?>
> > > 
> > > <!DOCTYPE web-app
> > >     PUBLIC "-//Sun Microsystems, Inc.//DTD Web 
> Application 2.3//EN"
> > >     "http://java.sun.com/dtd/web-app_2_3.dtd">
> > > 
> > > <web-app>
> > >   <display-name>Portal</display-name>
> > >   <description>
> > >      Portal 
> > >   </description>
> > >   
> > >   <taglib>        
> > >   	<taglib-uri>portaltags</taglib-uri>
> > >   	
> <taglib-location>/WEB-INF/taglib.tld</taglib-location>    
> > >   </taglib>
> > > 
> > > </web-app>
> > > 
> > > === The Java file ===
> > > package com.test;
> > > 
> > > import javax.servlet.jsp.JspTagException;
> > > import javax.servlet.jsp.tagext.TagSupport;
> > > 
> > > public class XeTestTag extends TagSupport
> > > {
> > > 	private String messageType = "0";
> > > 	/**
> > > 	 * Constructor for XeTestTag.
> > > 	 */
> > > 	public XeTestTag()
> > > 	{
> > > 		super();
> > > 	}
> > > 
> > > 	/**
> > > 	 * Sets the messageType.
> > > 	 * @param messageType The messageType to set
> > > 	 */
> > > 	public void setMessageType(String messageType)
> > > 	{
> > > 		this.messageType = messageType;
> > > 		System.out.println("MessageType: " + messageType);
> > > 	}
> > > 
> > > 	/** 
> > > 	 * Output the requested function.
> > > 	 * @return int
> > > 	 */
> > > 	public int doEndTag() throws JspTagException
> > > 	{
> > > 		try
> > > 		{
> > > 			pageContext.getOut().write(messageType);
> > > 		}
> > > 		catch (java.io.IOException e)
> > > 		{
> > > 			throw new JspTagException("IO Error: " +
> > > e.getMessage());
> > > 		}
> > > 		return EVAL_PAGE;
> > > 	}
> > > 
> > > }
> > > 
> > > --
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