Grails Add New Resources To MessageSource Dynamically

First create a groovy file with the following contents

package com.pkm.message.test

import grails.util.Environment
import javax.servlet.ServletContext

class MessageSourceCreator {
    public static def grailsApplication = null
    public static def servletContext = null
    public static def messageSource = null
    private static final String MESSAGE_FILE_DIR = "/WEB-INF/resources/messages"

    /**
     * @param fileName "some.message.properties"
     */
    public static void addNewMessageFile(String fileName) {
        String basePath = servletContext.getRealPath("/")
        fileName = fileName.substring(0, fileName.lastIndexOf("."))
        String relativeFilePath = "${MESSAGE_FILE_DIR}/${fileName}"

        if (Environment.isWarDeployed()) {
            messageSource.pluginBaseNames.add(0, relativeFilePath)
        } 
        else {
            String separator = Environment.current == Environment.TEST ? "/" : ""
            messageSource.pluginBaseNames.add(0, basePath + separator + relativeFilePath)
        }
    }

    public static void initialize(def ga, def sc, def ms) {
        grailsApplication = ga
        servletContext = sc
        messageSource = ms
    }
}

From BootStrap, need to call first initialize & then addNewMessageFile

/**
 * From BootStrap, need to call first initialize & then addNewMessageFile
 */
import com.pkm.message.test.MessageSourceCreator

class BootStrap {
    def grailsApplication
    def servletContext
    def messageSource

    def init = { servletContext ->
        MessageSourceCreator.initialize(grailsApplication, servletContext, messageSource)
        MessageSourceCreator.addNewMessageFile("some.message.properties")
    }

    def destroy = {

    }
}