Using XmlSlurper to update appengine-web.xml

I'm currently working on a project which is using GAE (Google Application Engine).
I wanted to setup Jenkins' jobs to update the different stages (acceptance, qa, uat) in our build pipeline.
To achieve that I created 3 different GAE's applications - one for each stage - and 4 Jenkins jobs: 1 template which holds the common steps and 3 others for the respective stages.
The first step of the template job updates appengine-web.xml target application and version based on parameters passed to the job.


See the groovy script below:

import groovy.xml.StreamingMarkupBuilder

//getting parameters values from environment variables
def env = System.getenv()
def workspace = env["WORKSPACE"]
def applicationName = env["TARGET_APPLICATION_NAME"]
def versionName = env["TARGET_VERSION_NAME"]
def ant = new AntBuilder()
ant.echo(message:"Opening $workspace/war/WEB-INF/appengine-web.xml")
def file = new File("$workspace/war/WEB-INF/appengine-web.xml")
def root = new XmlSlurper().parse(file)
ant.echo(message:"Updating appengine-web.xml with application: $applicationName and version: $versionName")
root.application=applicationName
root.version=versionName 
def outputBuilder = new StreamingMarkupBuilder()
String result = outputBuilder.bind{ 
   mkp.declareNamespace("":  "http://appengine.google.com/ns/1.0")    
   mkp.yield root 
}
ant.echo(message:"Writing appengine-web.xml")
file.write(result)