Gradle plugin for default properties - groovy

Question

I am trying (and failing :) ) to create a gradle plugin that has a default set of versions for dependencies and can be overridden in the gradle.build file that is calling my plugin. Ideally something like the sudo-code below
MyDefaultPropertiesPlugin.groovy
project.versions.springBoot="1.0.0-RELEASE"
MyPlugin.groovy
project.apply plugin: MyDefaultPropertiesPlugin
compile("org.springframework.boot:spring-boot-starter-web:${project.versions.springBoot}")
build.gradle
versions.springBoot = "1.1.0-RELEASE"
project.apply plugin "my.plugin"
I attempted to do using extensions but ran into isssue's via the ordering when overriding. (versions doesnt exist)
I would greatly appreciate any advise on this, maven would be easy, but my gradle knowledge is still evolving :)
Thanks in advance for any insight!

Answer 1

Plugins have to defer accessing the build model until after build scripts have been evaluated. Easiest solution is to use project.afterEvaluate {}, but there are others. For more information, see answers to similar questions here or on http://forums.gradle.org.

Answer 2

Came up with a pretty workable if not perfect solution, I will update if i think of anything better, my gradle is at a learning level, so please commend if this can be improved.
This allows me to define a set of versions and clients to overwrite those versions with a simple property
MyDefaultVersionsPlugin.groovy
class MyDefaultVersionsPlugin implements Plugin<Project>{
project.extensions.create('versions', MyVersions, project)
}
class MyVersions{
String spring
String slf4j
public MyVersions (Project project){
spring = setVersion(project,'springVersion', 'x.x.x.x')
slf4j = setVersion(project,'slf4jVersion', 'x.x.x.x')
}
private static String setVersion(Project project, String name, String version){
if(project.hasProperties(name)){
return project.getProperties().get(name)
}
else {
return version
}
}
}
MyPlugin.groovy
project.apply plugin: MyDefaultVersionsPlugin
compile("org.springframework.boot:spring-boot-starter-web:${project.versions.spring}")
build.gradle
buildscript { ext { springVersion = 'x.x.x.x'} }