build.gradle

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath('org.eclipse.jgit:org.eclipse.jgit:4.6.0.201612231935-r')
    }
}

import org.eclipse.jgit.lib.Repository
import org.eclipse.jgit.storage.file.FileRepositoryBuilder

import java.time.Instant
import java.time.ZoneOffset
import java.time.format.DateTimeFormatter

static def scmInfo(String path) {
    FileRepositoryBuilder builder = new FileRepositoryBuilder()
    Repository repository = builder.setGitDir(new File("${path}/.git"))
            .readEnvironment()
            .findGitDir()
            .build()

    def branch = repository.getBranch()
    def head = repository.resolve("HEAD")
    def revision = head == null ? "UNKNOWN" : head.name()
    def date = Instant.now().atOffset(ZoneOffset.UTC).format(DateTimeFormatter.ISO_OFFSET_DATE_TIME)
    def tstamp = Instant.now().atOffset(ZoneOffset.UTC).format(DateTimeFormatter.ofPattern("yyyyMMddHHmmssSSS"))

    return [
            branch  : branch,
            revision: revision,
            date    : date,
            tstamp  : tstamp
    ]
}

project.ext.scm = scmInfo(rootDir.getAbsolutePath())