JSP Fragments, jsp:include template text, variable placeholders : JSP

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01.09.2008 at 10:52AM PST, ID: 23070372

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7.4

JSP Fragments, jsp:include template text, variable placeholders

Zones: Java Standard Tag Library (JSTL) & Server Tags, Java Server Pages (JSP)

Tags: JSP

Can I use jsp:include or c:import in a jsp:attribute to set a tag fragment attribute and have it evaluate EL variables?

The following code does not work. The fragment EL variable to does not get evaluated by the tag handler. The output is
hello ${name}

when i was expecting
hello tony

I'm using Tomcat v5.5

         
           
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             Tag file: demo.tag
<%@ tag description="Demo tag" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ attribute name="template" fragment="true" %>
<%@ variable name-given="x" %>
<div>
    <c:set var="x" value="tony" />
    <jsp:invoke fragment="template" />
</div>
 
template.jsp
<%@ page contentType="text/html; charset=UTF-8" isELIgnored="true" %>
<font color="red">
hello ${x}
</font>
 
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
    
<%@ taglib tagdir="/WEB-INF/tags" prefix="and"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
 
<!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=ISO-8859-1">
<title>Demo fragments</title>
</head>
<body>
 <and:demo>
<jsp:attribute name="template">
<c:import url="/WEB-INF/template.jsp"/>
</jsp:attribute>
</and:demo>
 </body>
</html>

           
         

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Question Stats

Zone: Programming

Question Asked By: tony_murphy

Solution Provided By: araim

Participating Experts: 1

Solution Grade: A

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01.09.2008 at 11:11AM PST, ID: 20621158

tony_murphy:

Note:

I have set page directive attribute isELIgnored="true" so the included jsp does not have the EL evaluated, so it should be available to the tag handler?

01.09.2008 at 11:46AM PST, ID: 20621581

araim:

if you set isELignored to true, expression won't be evaluated, and you'll get hello ${x} instead of hello tony ... it's not what you've wanted ... is it?
also consider replacing <jsp:invoke fragment="template" /> with <jsp:include file="template.jsp"> it will simply build the resulting page by injecting code from template.jsp into the place where your jsp:include directive is (and also executing all the code in template.jsp and so on ... the plus is that you have all the variables that are abover the jsp:include directive available in your template.jsp also)

01.09.2008 at 11:57AM PST, ID: 20621688

tony_murphy:

Hi, thanks for responding.

I should explain more about what I'm trying to do. The example I have given is a very slimmed down version of what I'm hoping to achieve. I want to render content differently, the included jsp filename will vary based on the content I'm trying to render. It won't always be template.jsp. Apologies

                       
                                snip...
 
<body>
<and:demo>
 
<!-- generate filename for content rendering -->
<c:set var="filename" value="content.viewname" />
 
<jsp:attribute name="template">
 
<c:import url="/WEB-INF/${filename}.jsp"/>
 
</jsp:attribute>
 
</and:demo>
</body>
</html>

Open in New Window

01.09.2008 at 11:58AM PST, ID: 20621713

tony_murphy:

oh. forgot to mention - if I don't set isELignored=true, the included jsp page gets evaluated and ${name} disappears completely so the output is just

hello

01.09.2008 at 12:22PM PST, ID: 20621959

araim:

the deal with ELignored is as folows:
if you set the ignore to true, it won't evaluate any ${...} - none of them
the reason you get 'hello ' without anything is that the directive you are using does not extend the scope of variables to the imported page.
you do <c:set var="x" value="whatever"> and than use it in imported page, but in imported page this variable is null - it's not in scope so it doesn't display anything.
the <%@include however does extend the scope as , but it won't allow the ${filename} as it's param.

so.. what you can do is
<c:import url="${page}" >
<c:param name="wwho" value="VALUE HERE"></c:param>
</c:import>

the trick is that you have to use the values in an imported page as if they were posted (as parameters)
so you don't get to use ${wwho} but ${param.wwho} instead.

Accepted Solution

01.10.2008 at 12:34AM PST, ID: 20625726

tony_murphy:

Hi, Thanks for explaining this.

I believe that I can only pass a string using jsp:param. I guess it's back to the drawing board, as I need to pass another type of object.

I was hoping to pass an object to the tag and then have the tag render content using the fragment and evaluating the EL.

I will just have to put the object in request scope now that I think I have exhausted any hopes of a more tidy approach

araim

01.10.2008 at 12:40AM PST, ID: 20625750

you can always use session beans ... not sure, but perhaps page scope beans would also work...

tony_murphy

01.10.2008 at 12:45AM PST, ID: 20625760

Believe tag file only has access to application, session and request scopes from calling jsp page.

Scoping rules are unfortunately rather complex. Would have being nice if I could just have included jsp for template. Oh well can't have everything :)

20080236-EE-VQP-29 / EE_QW_2_20070628