Automatically compile different languages in GWT

How to integrate internationalization and localization into a GWT application? Assuming you're familiar with GWT internationalization, you probably answered "just put a language resource file into the appropriate source path, make sure your UI references these keys appropriately, and that you're using the Constants and Messages interfaces for everything dynamic". Fine.

Let's say you've done all that. Your application is fully internationalized. Now you want to localize it to three different languages, and I don't care what those languages are. You don't want to compile for all of those languages because that becomes a lot of permutations very quickly.

My default GWT compile is six different permutations per language. Three languages are 18 permutations, or 24 if you compile a "default" permutation. It takes me 10 minutes on my old computer to do just a six permutation build. I don't want a 40 minute compile, especially if I know ahead of time that whoever uses this application is going to want French only.

I'm also using ant as my build tool.

So I decided to take advantage of a little bit of automation.

Step 1: Create a new module file for each language.
This module file inherits the old module file and customizes the language only. Filename is App_2.gwt.xml.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 2.4.0//EN" "http://google-web-toolkit.googlecode.com/svn/tags/2.4.0/distro-source/core/src/gwt-module.dtd">
<module rename-to='app'>
    <inherits name="com.app.App" />

    <!-- Language specific compilation -->
    <extend-property name="locale" values="fr_CA" />
    <set-property-fallback name="locale" value="fr_CA" />
   
</module>


Step 2: Modify the ant script to build using this language file.
<java failonerror="true" fork="true" classname="com.google.gwt.dev.Compiler">
    <classpath>
        <path refid="project.class.path" />
    </classpath>
    <arg line="-war" />
    <arg value="war" />
    <arg value="com.app.App_2" />
</java>
I just changed the name of the GWT module that's being built, the rest of it's the same.

Step 3: Modify the ant script to copy the correct module over before the GWT compile even happens.

<copy todir="src/com/app" file="lang/App_2.gwt.xml" overwrite="true" />

All done. Now I can add new languages and all I need to maintain is a module file specifying which languages to include in a particular compilation. (And of course the language files themselves.)