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ConstantsTag
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Difference between version 10 and version 3:

At line 3 added 1 line.
Inspired by <a href="http://www.raibledesigns.com/page/rd?anchor=how_do_you_manage_your">this post</a>, I wrote a tag library to expose the fields of my Contants.java class to my JSPs. It allows a user to specify a single variable using:
At line 5 added 23 lines.
{{{
<appfuse:constants var="USER_KEY"/>
}}}
Or all variables:
{{{
<appfuse:constants/>
}}}
By default, it exposes the values from the Contants class imported into the tag library, but also allows a className variable to specify a different class. The main reason I wrote this was to prove it was possible. The second reason was to get around importing my Contants class (and using &lt;%=Contants.VARNAME%&gt;). With this tag, both of the following work:
{{{Scriptlet: <%=VARNAME%>, JSTL: <c:out value="${VARNAME}"/>}}}
The only thing it gives you over the import/scriptlet way is to expose the attribute to different scopes - i.e. page for JSTL. After writing it, I think it's a fairly useless tag library - I don't know if I'll ever use it, but maybe someone else will find it useful.
;:''BTW, you need to use it on the JSP you plan to use it in a scriptlet and you can't wrap it with oscache's &lt;cache&gt; tags.''
!Files Needed for Tag Library
* [1] ConstantsTag.java
* [2] ConstantsTei.java - exposes variables as attributes
----
!!ConstantsTag.java [#1]
At line 29 added 1 line.
At line 180 added 79 lines.
----
!!ConstantsTei.java [#2]
[{Java2HtmlPlugin
package org.appfuse.webapp.taglib;
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.jsp.tagext.TagData;
import javax.servlet.jsp.tagext.TagExtraInfo;
import javax.servlet.jsp.tagext.VariableInfo;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.appfuse.common.Constants;
/**
* Implementation of <code>TagExtraInfo</code> for the <b>constants</b>
* tag, identifying the scripting object(s) to be made visible.
*
* @author Matt Raible
* @version $Revision: 1.1 $ $Date: 2003/12/31 13:59:32 $
*/
public class ConstantsTei extends TagExtraInfo {
private Log log = LogFactory.getLog(ConstantsTei.class);
/**
* Return information about the scripting variables to be created.
*/
public VariableInfo[] getVariableInfo(TagData data) {
// loop through and expose all attributes
List vars = new ArrayList();
try {
String clazz = data.getAttributeString("className");
if (clazz == null) {
clazz = Constants.class.getName();
}
Class c = Class.forName(clazz);
// if no var specified, get all
if (data.getAttributeString("var") == null) {
Field[] fields = c.getDeclaredFields();
AccessibleObject.setAccessible(fields, true);
for (int i = 0; i < fields.length; i++) {
vars.add(new VariableInfo(fields[i].getName(),
"java.lang.String", true,
VariableInfo.AT_END));
}
} else {
String var = data.getAttributeString("var");
vars.add(new VariableInfo(c.getField(var).getName(),
"java.lang.String", true,
VariableInfo.AT_END));
}
} catch (Exception cnf) {
log.error(cnf.getMessage());
cnf.printStackTrace();
}
return (VariableInfo[]) vars.toArray(new VariableInfo[] { });
}
}
}]
Also see [my blog post|http://www.raibledesigns.com/page/rd?anchor=useless_tag_library].

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