build.gradle snippet for automatically adding version code postfix to APK file name

ApkVersionPostfix.build.gradle

import javax.xml.xpath.XPathConstants
import javax.xml.xpath.XPathFactory

// Set output filename of APK based on version code from manifest when doing release build
// Note: This script will add a couple of seconds to the build script build time
gradle.projectsEvaluated {
  preReleaseBuild.doFirst {
      android.applicationVariants.all { variant ->
          // Check version number configured in AndroidManifest
          if (variant.name != "release") return
          def dbf = javax.xml.parsers.DocumentBuilderFactory.newInstance().newDocumentBuilder()
          def manifestFile = "$project.projectDir" + "/src/main/AndroidManifest.xml"
          def doc = dbf.parse(manifestFile)
          def expr = XPathFactory.newInstance().newXPath().compile("/manifest/@versionCode")
          def versionCode = expr.evaluate(doc, XPathConstants.STRING)
          println "versionCode=" + versionCode
          // Set output filename
          variant.outputFile = file("../build/publish/myapp-v" + versionCode + ".apk")
      }
  }
}