Extract the keys from build.gradle

extract_keys_from_gradle.groovy

//build.gradle
android{
  ...
  productFlavors{
    staging{
      //use in java code
      buildConfigField "String", "SERVICE_THAT_I_NEED", getProps("service_secret_key")
      buildConfigField "String", "MY_BACKEND_URL", getProps("my_url")
      //use in xml, like AndroidManifest.xml
      resValue "string", "google_maps_key",  getProps("google_maps_key")
    }
    
    production{
      //use in java code
      buildConfigField "String", "SERVICE_THAT_I_NEED", getProps("service_secret_key")
      buildConfigField "String", "MY_BACKEND_URL",  getProps("my_url")
      //use in xml, like AndroidManifest.xml
      resValue "string", "google_maps_key", getProps("google_maps_key")
    }
  }
}

//We're going to use this method to read the secrets that
//we stored in out secrets.properties file
def getProps(String propName) {
    def propsFile = rootProject.file('secrets.properties')
    if (propsFile.exists()) {
        def props = new Properties()
        props.load(new FileInputStream(propsFile))
        return props[propName]
    } else {
        return "";
    }
}