android {
    ...
    def that = file('version.properties')
    Properties prop = new Properties()
    prop.load(new FileInputStream(that))
    if (that.canRead()) {
        prop.load(new FileInputStream(that))
    }
    def code = (prop.getProperty('VERSION_CODE') ?: "0").toInteger() + 1
    if (!that.exists()) {
        that.createNewFile()
        if (that.canWrite())
            prop.store(that.newWriter(), null)
    }
    ...
}