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Q: Access Java variable in JSTL tag ( Answered 4 out of 5 stars

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Question

Subject: Access Java variable in JSTL tag
Category: Computers > Programming
Asked by: jonra-ga
List Price: $5.00

Posted: 08 Jul 2004 04:13 PDT
Expires: 07 Aug 2004 04:13 PDT
Question ID: 371241

JSP/JSTL: 
I have a JSP page with some sciptlets

<%
String title="My page"
%>

I want to use <c:out value='${title}' /> JSTL tag to output the result.

Can I access the variable in the tag?

Answer

Subject: Re: Access Java variable in JSTL tag
Answered By: rhansenne-ga on 08 Jul 2004 09:02 PDT
Rated: 4 out of 5 stars

Hi jonra-ga ,

If you want to use a scriptlet to declare the variable and the c:out
tag to print it, a valid JSP page might look like this:


<%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>
<html>
<head>
<title>sample jsp page</title>
</head>
<body>
<%
  // declare or construct your variable...
  String title="My page";
  // set the variable in the page context under the variable name "title"
  pageContext.setAttribute("title",title);
%>
<c:out value='${title}' />
</body>
</html>


You can also declare variables using only jstl, in stead of through a scriptlet:


<%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>
<html>
<head>
<title>sample jsp page</title>
</head>
<body>
<c:set var="title" scope="page" value="My page"/>
<c:out value='${title}' />
</body>
</html>


Of course if you're using scriptlets anyway, you could also use the
following scriptlet to print the variable:

<html>
<head>
<title>sample jsp page</title>
</head>
<body>
<% String title="My page"; %>
<%=title%>
</body>
</html>

The jstl libraries should also be present in the classpath of your web application.

Here are some useful JSTL primers and references:

IBM - A JSTL primer:
http://www-106.ibm.com/developerworks/java/library/j-jstl0211.html

SUN - JavaServer Pages Standard Tag Library 
http://java.sun.com/webservices/docs/1.0/tutorial/doc/JSTL.html

JSP Syntax reference sheet:
http://www.oio.de/public/java/jstl-reference/jstl-reference-2004.pdf

Best regards,

rhansenne-ga.

Request for Answer Clarification by jonra-ga on 08 Jul 2004 09:21 PDT

Hi.

Thanks for your information.
I have an existing application with a lot of existing <%= data %>
outputs to the JSP. I have changed app server, and any value that is
null, prints "null" to the page. That's why I need to refractor my
code.

<c:out /> clean up the output and replaces null with "".
There are quite a few pages in the app, so I need to make the change
as smooth as possible.

That means that I cannot re-declare all the variables, as suggested.

Is there another way of passing in my existing strings into the tags?

Thanks,

Jon

Clarification of Answer by rhansenne-ga on 09 Jul 2004 15:29 PDT

Hi jonra-ga ,

Unfortunately, the c:out tag can only access variables which have been
placed in the page, request, session or application context.

You could however refactor your pages by replacing:

<%= data %>

by

<%= (data==null?"":data) %>

This would also ensure that null's are replaced by empty strings. (If
you know a little about regular expressions, this could even be done
by an automatic find and replace).


Sincerely,

rhansenne-ga.

jonra-ga rated this answer: 4 out of 5 stars

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