I found this post. There's a beta version being develop.
I've done what is suggested:
I added the mavenRepo
mavenRepo 'https://noams.artifactoryonline.com/noams/grails-jaxrs-plugin-snapshots'
And as I use the new Aether (Maven) resolver I configure the jaxrs plugin like this:
compile (':jaxrs:0.10-SNAPSHOT') {
excludes 'spring-core', 'spring-beans', 'spring-context', 'spring-web', 'spring-aop'
}
But org.restlet.ext.json:jar:2.1.4 was still missing so I also have to add this mavenRepo:
mavenRepo 'http://maven.restlet.org'
Application cleaned! Tests Passed!