Displaying Build Numbers in Grails Apps

Being a fan of Continuous Delivery, identifiable builds, and Continuous Integration: I like to deploy web apps with a visible build number, or some other way of identifying the version. For example, having the build number on the login screen for example. In the Maven/Java world, this is straightforward. Or at least I know the idioms. I struggled with this a bit while working on a Grails app,  and wanted to share my solution. There may be other, better, solutions, but the ones I found approaches that didn’t quite work they way that I’d hoped.

My requirements were:

I realized that that Grails itself changes the application metadata (application.properties) when it does a build. So I modeled this approach after code in one the gant scripts in the Grails distribution.
The steps are:

To create the event hook, create a file in your project/scripts directory called _Events.groovy that contains a method like:

 eventCreateWarStart = { warName, stagingDir ->
    def buildNumber = System.getProperty("build.number", "CUSTOM")
    println("Setting BUILD\_NUMBER to "\\+ buildNumber)
       file:"${stagingDir}/WEB-INF/classes/application.properties") {
         entry(key:"build.number", value:buildNumber)

Then you can access the property with a GSP tag like this
<g:meta name="build.number">

And you can now display build numbers (or any other properties that you want to pass in from you CI system) in your Grails app. This worked for me with Grails 1.3.7. The only down sides are:

I welcome any suggestions for improving this, or alerts that I’m using the entirely wrong idiom :)