Previously on my blog I described a workaround in passing data to JSF bean method. http://community.jboss.org/people/ilya40umov/blog/2010/12/28/my-favourite-workarounds-dummymap-for-jsf-12

It's very useful when you need some simple transformation with data which you are going to display on a page or compare with something using EL.

But now I've already found and tested the best way to do it. This way is a creation of the custom EL function which performs your transformation. This solution is very elegant but it's now new. I found a lot of posts on the Internet dated 2006-... about this topic. But I just want to show you my solution and tell you what didn't work for me.

My environment consists of Jboss 5.1 + Facelets 1.1.15-B1 + JSF 1.2.

I have a tag library based on facelets in my project. It was done accordingly to http://www.ibm.com/developerworks/java/library/j-facelets/.

So at first I want to tell you what didn't work:

• using of function declaration in my taglib.xml like it's shown below didn't get me any results

     <facelet-taglib>

         <function>

            <function-class>com.test.ElFunctions</function-class>

               <function-name>isInteger</function-name>

               <function-signature>boolean isInteger(java.lang.String)</function-signature>

         </function>

     </facelet-taglib>

• I had to create a separated library for functions because when I tried to define my custom tags in the same file as library-class it didn't work either.

Now about how it works.

1) Declaring library in web.xml

     <context-param>

          <param-name>facelets.LIBRARIES</param-name>

          <param-value>/WEB-INF/facelets/tags/test.functions.taglib.xml</param-value>

     </context-param>

2) I created taglib file (test.functions.taglib.xml):

<?xml version="1.0"?>

<!DOCTYPE facelet-taglib PUBLIC

  "-//Sun Microsystems, Inc.//DTD Facelet Taglib 1.0//EN"

  "facelet-taglib_1_0.dtd">

<facelet-taglib>

          <library-class>com.test.FnLibrary</library-class>

</facelet-taglib>

3) I created FnLibrary.java

import java.lang.reflect.Method;

import java.lang.reflect.Modifier;

import com.sun.facelets.tag.AbstractTagLibrary;

public final class FnLibrary extends AbstractTagLibrary {

          public final static String NAMESPACE = "http://www.test.com/jsf/functions";

          public static final FnLibrary INSTANCE = new FnLibrary();

          public FnLibrary() {

                    super(NAMESPACE);

                    try {

                              Method[] methods = FunctionsLibrary.class.getMethods();

                              for (int i = 0; i < methods.length; i++) {

                                        if (Modifier.isStatic(methods[i].getModifiers())) {

                                                  this.addFunction(methods[i].getName(), methods[i]);

                                        }

                              }

                    } catch (Exception e) {

                              throw new RuntimeException(e);

                    }

          }

}

4) And I created FunctionsLibrary.java

public class FunctionsLibrary {

          public static boolean isInteger(String value) {

                    if (value != null) {

                              try {

                                        Integer.valueOf(value);

                                        return true;

                              } catch (NumberFormatException e) {

                                        //ignore

                              }

                    }

                    return false;

          }

}

For using this library you just need to define prefix in your root element xmlns:tf="http://www.test.com/jsf/functions" and then you can use it in EL expressions.

So #{tf:isInteger('345')} returns true. =)

P.S. I used the following link for my final solution. It's completely based on this source. I'm just wondering why other solutions didn't work.

http://seamframework.org/Documentation/CreatingCustomELFunctions