class TestPlugin implements Plugin<Project> {
    void apply(Project project) {
        project.task('runPlugin') {
            group = 'application'
            def p = new SortedProperties()
            p.put("apple", "one")
            p.put("beta", "two")
            p.put("coffee", "three")
            def f = new File("test.properties")
            f.withOutputStream { stream -> p.store(stream, "Generated by the plugin.") }
            doLast {
                println "> cat ${f.name}"
                f.eachLine {
                    println it
                }
            }
        }
    }
}

class SortedProperties extends Properties {
    @Override
    Enumeration<Object> keys() {
        def keys = Collections.list(super.keys())
        keys.sort { a, b -> (a.toString() <=> b.toString()) }
        return Collections.enumeration(keys)
    }
}

apply plugin: TestPlugin
apply plugin: 'groovy'
apply plugin: 'application'

mainClassName = 'com.example.App'

dependencies {
    compile 'org.codehaus.groovy:groovy-all:2.4.14'
}

repositories {
    jcenter()
}

clean {
    delete fileTree(dir: "$projectDir", include: "*.properties")
}